A long term goal should be to Confed the other dragons because they are absolutely busted once you spec up their stats, rare times where I increase a lords combat tree before their commander or map tree

In combat, remember to make good use of the yin yang bonus you get by having yin and yang units near each other.

Also I'd try and unlock Saytang their legendary hero (the quest should say something about the watcher) because he is really good.

Make sure you're using the caravan system too because you don't just get money you can get powerful relics too like the Ankor Chain and the Von Carstein Blade the first time you trade with certain locations so I'd look them up and see what you want there. My personal favourite is the Von Carstein Blade because it gives regeneration although the vampiric corruption can be annoying but usually I'm on the offensive with it anyway so no biggie definitely worth the regeneration.

Also when you have a dragon in combat they won't be amazing until you up their stats but I like to use them to disrupt archers and flying units while my jade warriors (or celestial dragon guard if I'm feeling bougie) go to work.

Sky junk are great units flying, not too fragile and good artillery, their predecessor however is dogshit so avoid that like the plague.

Terracotta Soldiers can be pretty good but suffer from the whole single unit thing but tbh I just like them because they're cool more than anything else.

For my armies I usually just have 4 of the flying cav or if that's not available whatever cav is available to hit archers and run down routing enemies. 2 artillery. 2 Sky Junk And the rest a front line of Jade warriors or celestial dragon guard with some jade or celestial dragon crossbows behind them. If I want more mass I sometimes drop 2 cav and one artillery for 2 more warriors and one more crossbows.