IME, the #1 time bloat in running combat is waiting for people to make decisions. (That includes the DM.) For your own decisions, don't sweat the details: It's almost certainly better to make a fast decision than a tactically perfect decision. For your players, announce the person on deck to encourage them to pay attention and have a decision ready. If that's insufficient, start imposing declaration time limits.
(There's no need to be fascist about it: You're a human being not a computer or a chess clock. If the battlefield situation is radically altered and forces someone to look up a spell they hadn't anticipated using 20 seconds earlier, that's okay once in awhile.)
The #2 time bloat is poor bookkeeping. If you've got someone who has to re-calculate his hit bonus every single round then you need to make them fix that problem. (This includes people who are benefiting from a buff spell like bull's strength: Calculate your current number and jot it down somewhere.)
But poor bookkeeping also applies to the GM: Prep your encounters. If you're dealing with complex monsters, take a highlighter and mark 4 or 5 specific abilities you tend to forget or specifically want to make sure you use.
The #3 time bloat is waiting for information to be transferred. Keeping target numbers secret for a couple of rounds may be effective, but after that you're just wasting time: Tell people the magic number so that they can just tell you if they hit or not. (If they are waiting for you to tell them if they hit, encourage them to roll the damage while they're waiting.)
And, once again, this goes both ways: Prep a cheat sheet with the ACs of the PCs so that you don't have to ask for them every round. When the party gets hit with a fireball, tell them the Reflex DC and roll the damage while they're rolling their saves.
Similarly, encourage your players to give you all the information you need to resolve their actions without being prompted. (I've got one player who simply refuses to announce what the saving throw DC is for her spells. Drives me insane. When you say "I cast fireball", the next words out of your mouth should always be "the Reflex DC is X". There is never going to be a situation where I don't want to know that information. I've got another player who says, "I attack the orc!" and then waits for permission before rolling the attack roll. Why? I have no idea. But this kind of meaningless verbal by-play is a huge, pointless timesink.)