initially, send out gifts, give out wards, transfer vassels in their de jure territory, and maybe even give away one or two titles if you really need to. if a major vassel plots, imprison. thats one less revolt. make ABSOLUTLY sure yoy get a guardian with the education you want and good traits. stats are of secondary concern. you dont want to end up with a slothfull craven cynical envious deceitful ruler hated by all. once you manage to survive to your twenties or so, the fun starts. your short rule penalty is gone, you should have decent stats, and by the time youre 30 and have racked up some prestige and possible some piety by waging some wars, you should be liked enough to turn him into your best ruler ever because of the truly massive long reign and prestige bonus youre gonna rack up. thats possibly the greatest strenght of elective as well, elect a young heir and live till youre 70 and boast a +50 opinion bonus from long reign alone. never forget: the higher the opinion, the more levies(what is the great high ca vs low ca problem. guaranteed levies and more control again less revolts and LOTS UPON LOTS of levies if youre great).