DM Tips for a Better Dungeons and Dragons Campaign
Part 1: Gaming Environment and Ground Rules

1. Supply paper, pencils, and dice. Counting on the players to provide even their most basic requirements doesn't work, so don't try. Always have more sharpened pencils available than players. Bring lots of paper. Have more dice than you can possibly use.
2. Enforce a "No touching" rule. Some players can't resist touching the other players. This is disgusting and must be stopped before the other players abandon your campaign just to get away from the offenders. Declare a "no touching" rule and enforce it. Come down hard on even minor infractions, or when the game gets exciting, the offenders won't be able to control themselves and will be pawing and pummeling the other players like six-armed monkeys on acid. ("No touching" also includes "No pretending to touch, no brandishing, no looming over the other players" -- they need to stay out of each other's personal space.)
3. Enforce a "Hands off other people's stuff" rule. Players are not allowed to touch other people's posessions without permission, or read their notes, or use their laptops, or anything like that. In particular, anyone who knocks around someone else's lovingly painted miniatures should be taken out and shot.
4. Side conversations are okay, but should be done away from the gaming table. Suppose there are five players but you're DMing a situation that involves only two of them. What do the other players do? Well, frankly, if they aren't fascinated by the action involving the other two players, you're better off without them. If they can go off somewhere (not too far) and amuse themselves until it's their turn to role-play again, that's great. Better than having bored and figety players annoying everyone else -- relieves you of the burden of entertaining all the players all the time.
5. Keep notes in a spiral notebook. Or use some other method to keep your notes from scattered to the four winds. Loose sheets are horrible; tablets aren't much better (the sheets come out too easily) and three-ring binders are bulky and take up more than twice as much precious table space as a spiral notebook.
6. If you use a laptop for notes, set your editor to autosave very frequently. You won't like it if your computer crashes and you lose an hour's worth of notes. I'd set autosave to five minutes if I were you.
7. Have a break every hour. It helps. A lot. A 5-10 minute break adds a lot of pep back into the players and yourself.
8. Watch out for super-sized drinks. A single giant soda can destroy multiple laptops and a lot of expensive gaming books if spilled -- and they will be. Using a separate table for DM materials or banning large drinks from the gaming area can save some grief.
9. End the session before you're exhausted. If a gaming session runs late, I gradually stop taking notes, and the next day I can't remember anything that happened during the last hour or so of play. I guess I'm running on autopilot. This isn't good for me and it's not good for the players. Wrap things up before your performance (or theirs) falls off too much. Do something else if it's not time to go home yet. There's no law that says the whole session has to be devoted to D&D.
10. When in doubt, ask the players. Have you forgotten what happened in a long-ago session? Ask the players. Probably no one will remember the events exactly, but as soon as one player remembers something, another will remember another detail, and in a few minutes, the whole sequence of events will be recovered. Works like magic.