This has probably been covered in another thread but it has been awhile.

I would focus on happy buildings like watchtowers, border forts, militia buildings and churches; each one adds 10% to happiness. Also the builder virtues add happiness and you will almost certainly get them by building the above. I would also manually assign titles to make sure they are going to governors that don’t have vices that harm the happiness. I would also re-conquer a peasant province or 2 and “release all” until I get the occasional mercy virtue which adds 10% to happiness. And then a couple more and “kill all” until I get the +1 dread vice.

That’s all I can think of right now.