Well, I do not think the original poster wanted just “good DM and good players” – I will assume you already have good ones. We have a good DM in our group, and some good players, but have had bad (short lived) campaigns.
1) A good simple plot. Yes, you can have twists, but if you make your storyline a Byzantine mess of a million and one plot hooks, twists, turns, etc, it will leave both the DM and the players frustrated. For the DM, why create so much if you will be disappointed that they missed Cool Hook #47, or did not fall for Twist #22?
2) Interesting and colorful NPCs. Would the PCs rather encounter Hamlet, Indiana Jones, Robert Shaw/Capt Quint from Jaws, Joan of Arc, Clint Eastwood in The Good, the Bad & the Ugly, or a bunch of wooden stiffs? Would you rather have your big bad villain be a Darth Vader or Sheriff of Nottingham, or some bland wimp?
3) Starting slowly. If a campaign is meant to last, you will find out soon enough. No need to break out all the stops the first few weeks. Have a general plan of how Low Level Adventure XXYZ can develop into a long term campaign, but do not kill yourself for details right away. Maybe in week two, the players will decide, “Hey we hate this adventure/world, can we do something else?” But, if they are going for 4, 5 or 6 sessions, they will get attached to their characters and want the game to go on. As a PC, I always like to think back and say, “wow, and to think back that first week, a party of 4 goblins almost took out the whole party…”
4) Challenge the players, but do not overwhelm them. If the PCs have to face too many Run Away or Die situations, they will get frustrated. There is nothing better than in a big, climactic battle where everybody down to their last few hit points with everything riding on the next swing of your weapon or casting of your spell. We had a climactic battle once in a Conan world campaign where we had 4 unconscious PCs and 1 guy with one hit point left to drag the four guys out of the evil temple as it collapsed. That was good. (We make all our to hit and damage rolls in public on the center of the table, so no DM fudging on the damage)
5) For the players – try to work together and be heroes.
and i am quite serious.
