I tend to try to keep a slow but steady expansion going at all times; I'm almost always expanding somewhere, but usually only on one front at a time and against one faction unless I have other wars forced upon me (i.e. a faction attacks me or the Pope orders me to go on Crusade). I tend to be quite leisurely about it, taking about one city every two turns or so after the initial firestorm against the local rebels. It's usually enough expansion that I tend to win the Long Campaign conditions around the 1250 mark.

I also tend to be quite picky about where I will expand; I like to snap up little islands such as Crete, Cyprus and Ireland, and to carve a colonies out of factions quite some way away from my main empire. As such my empires tend to end up quite far-flung and disjointed, with all sorts of funny shaped peninsulas only loosely connected to the central provinces.