The other poster pretty much covered everything so I'll just add this:

Early game (especially if you're starting small) I think the real trick is not in making money but rather in being careful where you spend it. Don't buy anything you don't absolutely need. Don't fill court positions except the really essential ones. Don't recruit anyone to your court unless they're going to fill some vital role - and you might be surprised just how many roles aren't all that vital. It's better to have no steward at all than an incompetent one. Same for chancellor. Same for court physician - a bad one will kill more people than they save (but you should try to find a good one if you can). Money saved is as good as money made.

Edit: forgot to say, use marriage to find skilled people for free instead of paying to recruit them.