After played several games as China, I have a good direction to what a China player needs to play.
But first, let's take in the situation.
China starts off with a large amount of militia units, some infantry and destroyers and one plane. With the economy, it's much better than Italy and Brazil, not to mention its economy is on par with European France.
Geographically, it's surrounded with weak nations on their own (Mongolia, Xingiang and Tibet), Japan and a single AI as a buffer between Mongolia and Japan.
To begin with a game as China, it's best to check the relations with Japan and always demand share map. If Japan refuses or makes suspicious buildup on your border, then you know you need to hold a defense. Despite Japan having a strong navy, it cannot create enough of a force enough to counter a dedicated NRA on full production.
Next is Mongolia and Xingjiang.
A Nationalist China player should focus either of these two nations first if Japan is on good terms with NC or it is clear that the nations is going AI.
Finnally, there's Tibet, France and Britain.
Do not focus your invasion on the latter two, as the resources gained aren't as profitable than the two nations mentioned above. As for Tibet, guard your borders with some militias.
For army tech, focus on building lvl 2 infantry & artillery (not too weak as lvl 1 and not too long and expensive as lvl 3), create lvl 1 armored cars and tanks from Chengdu for combat to Mongolia and Xingjiang. Do not focus much on air force, as the cost to research and build up a squadron would not be as great as a couple of artilleries and infantry.
For industry, focus on building Chongqing, Ziyang and Xuzhou. Then build industries on steel/rare material provinces (double resource in cities & provinces that makes 1500 on 100% morale) if running short of them. Try not to build industries on provinces directly bordering Japan unless you can handle it.
As for diplomacy, it is up to you how you set it up. China is second to Japan as the most powerful Asian country, so it would be a valuable ally for western nations to have, especially if they're at war with Japan.
And that is it for starting China for the first week. Now, there's a lot of people who have their own version as to play China, and so I created this post of a China more reliant on artillery, infantry and armored vehicles.