Designate certain provinces for your nobility estates. Find places that don't have high trade power, goods which have low trade value, and not many 'goods produced'. Basically some place that produces grain, or maybe fish, etc. Try to find a place that's either farmland, or plains. Build manpower buildings, and develop MIL to max. A typical place would be like 5-5-11, for example. Or maybe you go to +30, and it's 7-8-16. Give those to the nobility, and you're manpower will skyrocket.
Trade cities, which have 'inland/coastal centers of trade', estuaries, etc... the burghers get these (boosting trade power & income), and you focus on production development here, with production buildings. Maybe Hamburg for example, is a 9-18-8. All that development in these provinces gives you even more trade power. Build your first manufactories here.
You probably won't have much admin pts to spare, but if you can manage to have some 9-4-4 prov's for ex., the clergy can give you some good tax income enhancement there. Churches/temples, needless to say.
The time to develop your capital is ONLY when you're trying to get a new institution. Save it for that. When you develop the capital, the institution boost is much greater there, than in your other provinces.
I typically develop most when I extort my estates every 30 years... when the burghers are above 60 loyalty. Do as much development as you can at that time... but of course don't interfere too much with getting tech on schedule. Tech generally has priority.
Needless to say; only develop where it's a state, and preferably accepted culture. The exception would be: gold mines. Keep bumping that production, if you need the cash.
But yeah... development, is actually what makes an empire great. -And then the ability to fully utilize that development (right culture, religion, be a state, low autonomy, etc.)
