I also try to develop a few really good generals, since my gaming style usually includes only smallscaled, focused attacks which usually aim to snatch a few provinces at a time, then develop them, move in a garrison and then continue the invasion or move the conquering army somewhere else. With this style, I don't expand very quickly, but I think it's only good, since then I have time to use those units coming available on high/late (I always start on early) and lets the AI factions grow bigger so they give a bigger challenge to me
I try to keep my borders as short as possible so that I have very few provinces that need to be defended. I have found this tactic really effective, since it reduces the army upkeep and enables me to keep most of my generals in the frontline conquering new provinces. With this tactic it is important to find those key provinces that are easy to defend with as little troops as possible. Some nice ones are e.g. Kiev (bridge) and Navarre and Aragonia (mountains). I think there is a coplete list of these "special" provinces in the numerology thread in the .com.