Keep being at crushades, and make war taxes. But you need good admin ruler for this. Invest all money into production tech, don't take decisions which reduce your taxes, take beaurocracy as first NI. I mean if we mean no trading, beaurocracy is very good. Also, conquer all cores you can. Build only buildings which increase demand or increase your economy directly, plus goverment buildings. Gov buildings you will need to spam colleges, so that you can build all possible buildings in the end. Take sherrif and alderman advisors, when you grow big enough. When it comes to protestantism, convert to protestant. And allways try to keep stability at +3.
If you will have all gov buildings, and spam colleges, you will be able to build all buildings you want, and then destroy colleges, to build mints and treasuries. Keep being at war if you own iron and/or cooper, stick at least 1k in every grain province you can (even if not your province), to decrease supply(will not decrease your production - actualy increase it), so the supply/demand looks better.
If you are scotland : keep fighting england.
Rush gov tech 10 when you are close - then take the decision in capital, for 5 magistrates, to formalize scales and measures. Will give you +10% TE&PE and +5% taxes