First step is knowing the problem or problems. Do the players spend too much time deciding their next move, or do not pay attention until is their turn and then you have to explain hem what happened this round? Calculating things take too long? Miniature dancing (I move here. No, here. Wait, I draw an AoO, so here. No...)? Are the players confused about where and who's everyone, and how's the environment, and you have to clarify it frequently? Rules arguments? Adjudicating effects of spells, or reading their entries, take too much time? Player's don't know their character's abilities, or don't add all the bonuses until they have to roll? Do you spend too much time managing NPCs' stats or game variables (substracting hit points, calculating spell durations, checking who's stunned/nauseated/managing initiative order/etc...)? Or is it something else?