I didn't think describing in great detail how someone would go about deliberately destroying a country from within, until I realised if I did then people could easily recognise the signs and see it being done to their own right now. In no particular order you would (any or all):
Reduce freedoms including:
Movement: Make it expensive to travel, whether by car or public transport, by raising fares and fuel, plus taxes on both. Then restrict the roads by narrowing them and damaging them with concrete blockages on or by the road reducing the speed of cars to almost walking pace in order to avoid causing damage or accidents. Deliberately force cars onto the wrong side of the road to encourage them to either avoid such roads entirely or cause an accident. Then start banning cars altogether, as they have begun to in Paris, and in London for older commercial vehicles so far. The Liberal Democrats want to do this entirely in Britain in 2040 although as lame ducks would need one of the major parties to support them to get it through.
Speech: In Seattle certain words and phrases are now illegal, while in Britain professional bodies and councils will sack any staff heard to use any word like spastic, backward or anything connoting race outside the words designated by them, despite most being technical terms previously used in the medical profession and general usage. In the end the press and citizens in general will be so scared to be heard using the wrong words in public they may avoid mentioning certain subjects like immigration and local crime altogether, while both rise like rockets.
Morality: If I'm not hurting anyone then whose business is it who I have sex with or what we do? Or talk about, encourage or otherwise promote any forms of harmless and natural activities? So although it's nigh on impossible to prosecute someone for oral sex, making it illegal as in some US states probably deters many people, but why? They may have religious reasons but in Britain there are plenty of other areas of life censored and banned by laws old and new, including many relating to prostitution. Rather than legalise and regulate it it carries on regardless but run partly by organised criminals who pay off the authorities to profit from it underground. The more you impose on people's morals, which by definition are personal and not universal, the less freedom the people will enjoy.
Building: In Britain it can take 10 years to get permission to build a new public building, and 20 for a new station or airport, while the Chinese have built three of each including permission in the same periods. It's fine to zone areas to keep the density thin and industry separate from housing, but more than that (despite allowing rooms with no windows or room for furniture) the size and style should be entirely free for the owner to decide, up to certain limits. But make it unreasonably difficult to build and you open the doors to bribery and corruption, and end up with similar buildings anyway as long as the correct palms are greased, but for far greater cost and delay.
Making life difficult for people, although everyone would prefer a free run either along a road or through life in general is cruelty for the sake of it, making impossible excuses such as safety and security, to justify actions large and small which make the poor suffer the most in sales taxes and ration their use of travel and heating as they spend more of their total capital compared to everyone else on it. And try and make food expensive to, maybe by making it the law to burn 20% of corn on fuel instead of coal and oil.
Give rights to criminals: When a burglar enters your property then they have violated your rights in every potential way, yet they still have them, often more than you do. Why not simply make it almost impossible to try and stop a burglar in any effective way by allowing the police and victim to prosecute you instead of vice versa. That shows the side any government is on offering criminals such rights. And allow immigrants to enter regardless of the crimes they have committed or been accused of in their own countries, even allowing fugitives from the law to seek asylum and offer them benefits and council housing above people who have been waiting for years. Then do your best to hide the ethnic and cultural origins of the organised crime gangs once some are caught and reported in the papers, so again the victims look more guilty than the perpetrators for daring to suggest allowing gangs of foreign criminals in deliberately in the first place is actually an act of treason.
Debase the currency: Currency wars are the tool of the lazy government everywhere, instead of competing fairly an exporter will do all they can to reduce the value of the currency to make more profit on the same goods, while raising the commodities traded on the world markets in dollars almost beyond the means of normal people to afford as a result as the dollar rarely drops. Then create vast amounts of inflation through printing money, as in pre-war Germany and current day Zimbabwe, so whatever savings people have gradually becomes worthless while bankers and traders hedge against the falling currency they lobbied to create, making them the net recipients of everyone else's losses. Keep the interest rates at rock bottom to reduce everyone's pensions and savings and force up house prices as they are fuelled by cheap borrowing which only causes inflation, and again people are forced to spend more buying a house or renting and less on everything else, while the bankers and governments take it in cheap money to invest for themselves.
Infiltrate the authorities: Like the mafia, if each authority from the judiciary, government, civil service and police contain a scattering of Dons, then they can work together as a smooth running machine and protect their own and carry out organised crime with very little chance of conviction, as the chain of justice will be broken at any point, from witness to judge and between, while the top men are allowed to run any businesses they like without any threat from above, as they are at the top with no one above them.
Propaganda: If the government own or run the press behind the scenes, they will both promote shady businesses and policies, and use it to ridicule or block any opponents to any corruption seen in the system. In the end (although the internet makes this harder and harder) you can pretty much close down certain subjects being mentioned to the minimum, whether 'legally' through fake injunctions, or stick and carrot methods used by the mafia, allowing the people to rarely get a clue what is really going on besides what the governments want them to know and think. Whenever someone pops up with the truth ridicule them, if that doesn't work threaten or smear their reputation, and then if necessary find them dead by a mysterious accident.
End free trade: If you make cheap foreign or even home produced goods expensive through tariffs, or find ways of banning them altogether, then the people will have to pay far more than they really need to. If necessary use excuses like saving the environment or anything else the people could never discover directly for themselves just to keep some social order in place. Then add a profit into all public services which are not open to competition and allow companies to profit needlessly for essentials like water and electricity which can only be provided by a single system whoever you pay up front. How many water pipes enter your house to choose the best, and when you do what's the difference between the water in one or the other? Then manipulate the commodity and currency prices through false bids, inside trading and every other means known to the industry and you can raise and lower most prices at will within reasonable boundaries.
Restrict invention: If you make laws banning engines over 80% efficiency (check current US patent regulations) or anything else needing far more testing and regulation than required, many simply won't be able to find or afford the added costs and end up being bought for pennies from rivals who will simply save them till their own business model becomes obsolete. And when nothing legal works and they manage to go ahead anyway simply revert to plan B as with the whistleblowers. After all, if the people become rich and powerful who would need governments to run them and look after them when they can afford to live and travel cheaply and easily?
Poison the ecosystem: If there was no reason to do it, spraying toxic chemicals over vast areas of land would be one of the few things likely to cause a revolution. But tell people it's necessary to block the sun from burning the planet (you know, like it did before they started), then say it's only a theory and never mention actual activities (they fly high enough to be impossible to catch specifically) who could ever prove it, besides some lucky random scientists who took samples and were then dealt with by the propaganda machine to make sure their findings never got beyond the internet. But bees and fish and birds die in thousands and no one can imagine how or why. Then better still get into the inside of the ecosystem itself and alter it genetically. Then either the seeds are sterile and sold to the third world as cheap food but can't be reproduced so must pay another company annually for a new crop indefinitely, using the monopoly system of pricing, or if not sterile can make all nearby crops spread whichever alteration you have inserted over a larger and larger scale over time.
Divide friends and family: One of the oldest and best, if you think of policies and ideas which can be taught to children, for instance, who then turn against their parents unaware of such bogus policies, then the government and education system will become more powerful than the parents. Tell a generation of schoolkids to tell their parents to cut their carbon footprint (potentially allowing them to get hypothermia if followed to the letter), and it will not just create some massive rows but actually make children suspicious and wary of the motives of their own parents. Add a course in political correctness and then you can also have children accusing their parents of being racists, and ideally reporting them to the authorities for it. And of course touching children must be illegal to reinforce the breaking of the bond between parents and their children, and their nurses and teachers as well. And if any are caught doing so then make sure the press report it immediately with names and pictures even if they haven't even been charged yet, to further divide the community. You can also deliberately allow in hostile groups to take over small communities from abroad, such as Romanian crime gangs, and then accuse the entire town of being racist when they complain about thefts and vandalism etc. It works every time. And create outlandish theories about the world no one can prove one way or another, and watch friends and families fight over them, like gay marriage or global warming, where no issue ever existed beforehand but you manage to create one from thin air.
Restrict wealth: Make it almost impossible to become rich by vast progressive taxation and put everyone off trying or find ways of cheating. If you want to be inventive think of grand ways of spending the money on everything except what the people actually need, like cable cars, cycle lanes and road humps while the roads themselves actually decay and there aren't enough bridges to get across the rivers. And then charge to use the ones there are.
Charge for becoming ill: People have little or no control over becoming ill, but charge them for treatment anyway, and if it makes them bankrupt and lose their house it's just bad luck.
Overpopulation: Allow anyone and everyone to come to the country, and advertise in particularly backward and obnoxious countries to get some of the very worst and criminal gangs, who then barely speak the language and form tight pockets of local groups keeping separate from the local people and then employing each other and sending much of what they earn abroad. It clogs up densely populated areas and stresses public services on both infrastructure and personnel. So what if everyone has to wait twice as long for the doctor and dentist, if they can actually find one. And it takes twice as long to get everywhere as there are so many more cars on the roads which you haven't increased and narrowed already to reduce the flow of traffic.