I always do my best to keep the game moving. Once I have the players' attention, it can be really hard to get it again if the game stops and they get distracted.
I ask my players not to argue with me about my interpretation of the rules while we're in the middle of the game, unless a PC's life depends on the result. We can discuss the rules after the adventure (or on a break) and keep it in mind for the next time.
Preparation can help a lot. If I have the time, I do all of my maps in CC3 (even the ones in a module, if we're playing a module) and print out the important areas at the 1" = 5' scale. For dungeons, I prefer to print out the entire thing, regardless of whether combat happens in that location. It helps the players if they're mapping and saves time of having to re-read room dimensions again and again. It saves me the time of having to draw everything out on a battlemat -- and quite honestly, marker scribbles on a plastic or rubber grid don't really do it for me visually. The CC3 maps look better (and can be in colour if I'm not feeling cheap) and take virtually no time to use in play.
I keep a record of all of the PCs' important stats handy -- combat modifiers and skills that I may need to roll for them. It saves me time from having to ask them, and also avoids "Hey, what's your Spot check modifier?" "Plus 8" "Okay... You don't notice anything."
If PCs have unusual items, feats, or other abilities, I make note of those on the above sheet(s). Generally, I try to have as much of the PCs' info on-hand as I can and arranged so that I can access it at a glance.
I rarely run a combat straight out of the Monster Manual. If I have time beforehand, I'll write out the salient combat bits on the piece of paper that I'll be using to run the combat (or even do it quickly while the PCs are discussing amongst themselves).
If an NPC, monster, magic item, etc, is going to be important throughout the whole adventure (or longer), I'll prepare a 3x5 index card for it so that I can keep it handy at all times.
It's just part of my DMing style, but I favour the approach of fewer but more challenging combat encounters. 13-14 encounters per level that use approximately 25% of the PCs resources bores me to tears -- that's including the one or two intentionally difficult battles assumed by that model. A challenging battle usually takes longer to run than an "average" battle, but it's faster than running 3 or 4 "average" battles. Watching the PCs fight for their lives in most of their battles is far more exciting.
I make sure that I include opportunities in every adventure (and in most complex encounters) for every character to shine. When a player zones out because there is nothing for his or her character to do other than "uh, I shoot it with my crossbow because I'm out of spells" or "uh, I guess I keep singing" then when it comes time for that player to actually be able to do something, the game stalls while he or she is deciding what to do. He or she is completely out of the game, often needs to have things re-explained because they weren't paying attention, and often spends several minutes flipping through books and looking at his or her character sheet trying to find something. I can't say I blame the players when this happens -- when I'm a player I'm the first one to start spinning dice and looking at things for the next character I want to make when there isn't anything for my character to do. So if I keep all of the players more-or-less equally involved, this happens much less often. Bored players almost always end up causing the game to grind to a halt because they weren't paying attention.
It probably helps to limit the number of supplemental books that the players can use for creating their characters. It sucks up time when a player needs to look up the specifics of a particular feat or spell and has to flip through four books to find it. I'll often provide the player with a page or two of the relevant class/feat/etc info from a supplemental book (that one of us owns) to keep with his or her character sheet to avoid having to look stuff up.
I make heavy use of these reference sheets:
http://www.angelfire.com/rpg2/dnd3e/documents/refsheets35.zip. I give each player a copy of the player's combat reference sheet, which includes all of the combat actions, what they do, and whether they are standard or move actions, as well as other useful stuff. One of the sheets in that package also provides a summary of all conditions and their effects. It's not a substitute for having read the rules, but it's a real time-saver while playing the game.
Again, the more pre-game preparation that I can do, the more smoothly the game seems to run. If I'm running a module, I make sure that I've read it several times (or at least the parts we're most likely to hit that night). I try to get battle mats printed out in advance (or use pre-printed tiles to build something that's close enough to work). I start "encounter sheets" for each combat that I anticipate will occur.
Basically, anything that you can do to minimize the use of the books (or more than one or two) while playing is extremely helpful in keeping things running smoothly. If I'm running a module and don't have time to make encounter sheets for everything, I'll photocopy the monster stats listing from the back so I don't have to keep flipping. Same thing with maps, if the cover is stapled onto the module.
If you have a notebook PC and take the time to organize your files, it can be a big time-saver as well. I don't like players having computers at the table, because they inevitably stop paying complete attention to the game.
Hope you find some of these ideas helpful!