China is a monster, yet almost defenseless. Remedying this situation will require you to deal with vast national unrest; ignoring it will result in piecemeal absorption. Your advantages are limitless resources and vast tracts of land; like Russia, China can afford to trade space for time.
China is a challenging nation to play, though capable of reaching the top ranks if played correctly. The key issue is uncivilised status. A civilised China, with its terrifying manpower, coal and iron reserves, and isolated strategic position, is easily capable of dominating a game.
China in SP
In SP games, uncivilised status is fairly easy to get rid of. You need 10 MIL; you start with 7, and can easily afford another thirty irregular divisions. You need 100 prestige; annex Tibet or Siam, uncivs like yourself and easy game for your vast (if badly-trained) army. Finally, you need 50 IND. That means you need factories, which in turn means you need Publishing Industry (and its prerequisite Water-wheel Power) at the very least. The quick way is to trade for it; give away your useless claims in Sakhalin and some money. However much money is required. With full tariffs, you'll have money pouring in in job lots. Build as many factories as possible, cheap ones using only one or two Machine Parts; for now, don't worry about profit - your priority is to reach civilised status. As you can afford it, build more colonial claims to trade for more techs. Build a navy; it is not impossible to grab British Australia in the Opium War, though you will probably want to avoid pitched battles with the Royal Navy.
While this is going on, you will no doubt have to deal with the Opium War. You have a choice to make here : Do you want the event chain springing from a loss? Against the AI, you can almost certainly hold out by simply smothering it in bodies; after all, you start with 1500 manpower. There are several treaty events giving you negative prestige if you lose the war, which is a handicap on your way to civilised status. There is also another war, the Arrow Incident, which is not triggered if you have won the Opium War. On the other hand, there are also some 'self-strengthening' events giving you a fair number of random technologies, which can be useful. Civilised or not, you are going to be behind on research, since you start with no technologies at all. While this can also be remedied through tech trading, events with six (!) free techs are always nice.
Once civilised, you are free to run rampant in Asia. Create an empire in Indo-China? Probably already done as a stepping-stone. Drive the British out of India? Build a hundred regular infantry divisions, mobilise another two hundred, and laugh maniacally. Push the interloping Russians back to the Urals? There's always more peasants where the first lot came from. You are the rightful ruler of All Under Heaven; any problem can be buried, if you throw enough bodies at it.
Some hints when playing with China
- Hold your first tech trade until "interchangeable parts" is available. With some luck, nations like USA will have interchangeable parts at 1841. This give you 10 machine part and trigger Precision Work-invention which give you another 10, and, the most important, you can build machine part factory now! Fully industrialize at early 1850!
- Claim as many colonies as you can. Keep buying cement, lumber at the early beginning. Ryukyu, Bonin Island, Sunda Island and Sakhalin are the first targets. This give you a boost in prestige, enable you to buy goods easier in WM, thus you can keep importing cement and lumber to expand your colony empire.(Build colonies in Africa is very interesting). Also you can use those claims to trade tech to save money. Claim colony is the only way to increase Chinese prestige as China lag behind much in Culture tech, and defense spending is too expensive to maintain at high level(at early beginning)
- Don't hesitate to throw a few irregulars to seize British colonies all over the world during the two Opium war. It is possible to rise the yellow dragon flag at New Zealand and Australia, or even Canada. Even if you fail, losing a few irregulars and transport is nothing for the huge Chinese Empire.
- Attack all uncivilized(or even civilized) nation with prestige under -300. Annex them and use their land to trade claim. more Land and POP are not necessary to huge Chinese empire, but claiming colony can gain prestige, so trade for it.
China in MP
Multiplayer is a much greater challenge. The other players are certainly aware of the potential outlined above. If they have any brains, they will organise a tech embargo, and house rules against tech trading with AI nations are not uncommon. At the same time, humans are much better at exploiting China's initial weaknesses than the AI is. Your armies, though large, are pathetically bad; your main strategy should be to pour hundreds of thousands of troops into provinces the enemy is trying to occupy, and watch their troops attrite away at the end of the month. Of course, this only works on defense, but that is all that should concern you for the first few years.
You may be able to avoid the Opium War through diplomacy, but expect to give up many provinces in exchange. If Russia declares war, win it at all costs; if you give up even a single province, an event will take the Amur watershed, with its large coal and iron deposits, away from you. You may find it useful to ally with the Ottoman Empire, another backwards nation threatened by Russia.
Your main problem in becoming civilised is again the industry rating. You should expect the tech-trading route to be closed to you, which means you will have to employ brute force : Promote clerks until you are producing 0.2 to 0.5 RP a year. For an unciv, that is a very large amount of clerks, indeed; China is perhaps the only nation capable of the feat. Research industry techs and build cheap factories, preferably in the same areas you have your clerks. Promote a few small craftsman POPs. Bide your time. When you do become civilised, laugh maniacally, build an enormous number of regular divisions, and attack British India. Death to the round-eyed devils!
China in Victoria: Revolutions
Disclaimer: OK, I seriously just cut and pasted this from a post in the Paradox forum, so it's hardly official. It's still sound advice, though. At least it should be.
A few changes. You need 25 Military and 75 Industrial in order to civilize in Ricky (shorthand for Victoria Revolutions for you newbies). Also, you can't exploit cheap an' early colonial claims in Ricky, so you'll have to do it the old-fashioned, semi-plausible way. Or my way, as I like to call it.
1. Trade with Russia in order to get Publishing Industry, and at least one more military or economic tech. Build up relations with Russia at first (give them 100 pounds instead of just building influence; it's cheaper and faster, and you have very few diplomatic points as an uncivilized nation), but make absolutely certain that if you're going after army techs, that you get them by 1840. You don't need to research anything else; don't waste your first research slot if there isn't anything good to research, or else you'll be stuck for decades. Change your research institution if you absolutely must, but be very careful about the Prestige loss. So, in order of urgency: Publishing Industry, Practical Steam Engine, Mechanical Production, any other army tech (except Artillery), any other economic tech. Cultural, Naval, and Army Artillery techs are 100% worthless until you civilize.
2. 25 Military is no problem. Buy Small Arms and Canned Food off the World Market; it shouldn't be too hard. You'll need those Infantry for something more critical than building your score. Build as many as the Market and your treasury will allow you, and put them in the Guangzhou and Shanghai areas.
3. Assuming you don't lose to the British (which will happen if you lose enough provinces), Prestige won't be a problem. Just keep funding Military Spending until it's high enough, and always pick the +Prestige random events. What else are you gonna spend your money on?
4. If you've been at war with the UK for years and they haven't taken a single province from you, but still won't grant you a White Peace, you can use F12--->neville to get yourself one. You can even neville yourself HongKong if they took it from you. It's only fair.
5. Build as many 1 Machine Parts factories as you can. You'll probably need to wait for the Market to open up in order to get all the Machine Parts you'll need, and that would probably take until the 1870s, so all you have to do is fight off the British twice until then. DO NOT lose either war...
...unless you like playing on Hard mode. And kudos to you if you do; there's nothing wrong with playing a little historically. You'll have plenty of time to steamroll the world once you civilize.