Try playing on hard or expert first if you haven't already.

After that, I like to think of a 'theme', and stick to it
1) Snobbish aristocracy - cannot recruit peasants in any province/ every army must have an aristocratic unit

2) Isolationism (works best for non-catholic powers) - No emissaries, no religious figures, decline all diplomacy. assassins okay if you want

3) Pillager - must destory all remaining buildings in a newly conquered province (excepting provinces you held for some time then re-acquired).

etc.