1: Have a plan, but be Adaptable. Things change, people do unexpected stuff once the campaign starts, or can't show up on a given night, or whatever. Be ready and willing to change the plan, but have a plan in the first place: It helps.
2: Plan a story, but not too much. Have a story laid out, but don't plan down to the most minute detail: Enough that you know where you want to take it, but not so much that you won't get fouled up when some character gets creative and doesn't follow the script, or some other change seems like a good idea. See tip 1.
3: Have a real story. Make it more than another AD&D-style beat-the-villians campaign; have an honest-to-goodness plot that would be worth following to see what happens. And it doesn't have to be heavy-action: Don't be afraid to inject some or a lot of humor and character development/interpersonal events.
4: Tailor your tale to your players. Once you know who's going to go, try to include reason for them to be interested in the plot. More than just 'we're under attack' or 'we're trying to get home', if you can work in stuff that would be especially motivating to your participants, and specifically give them chances/opportunities to develop, so much the better. Also, conversely, try to get characters involved that suit the story: If there's a lot of heavy action, for instance, the local hairdresser might not be the best person to bring along.
5: Avoid gratuitous fight scenes. Done right, a good, rock-'em-sock-'em fight to bring down the bad guys can be fun. But don't overdo it, and try to avoid action for action's sake: Have confrontations that advance the story somehow, or bring in some important NPC.. or (use sparingly) to help 'set the scene', if you want to give the impression of a locale in turmoil.
6: Don't be afraid to stylize. In the real world, stuff happens by accident, or by chance. This is not the real world. In a well-run plot, every action, every NPC you bring in, and every spoofed bit of scenery should have a point. Don't let anything happen by accident. Everyone you introduce should have a reason for being there, and be given stage-time and attention in proportion to that reason: Feature Characters should get lots, the anonymous shopkeeper with the important tip should get a few minutes; and that crowd in the background should only be there to give the feeling of a busy city, unless it's a riot mob. ;)
7: Give your NPCs a life. Okay, if someone's on-stage for all of two minutes, they don't need much background. But everyone should have as much motivation as is needed to explain their role (ie a merchant just wnats to make a profit selling stuff, or the ninja that helps them is out to avenge his family). Major NPCs should have a fairly well fleshed-out personality, set of motivations, and at least some background/history. Be sure that any history fits with whatever motivations you give them.
8: Be consistent. That's as simple as it sounds. For instance, if the hotel they were staying in was in a nice neighborhood to begin with, it should be so at the end of the story, unless you give a reason. This is especially important with feature NPCs. Keep their behaivior consistent with their motivations, and if you're going to change them, have a reason (some traumatic event, etc.) why.
9: Coordinate. Talk to people. For instance, if possible, set up ahead of time when you and the other folks involved will be on-line: this especially helps keep offworld plots from dragging on forever because 'we had everyone but Bill tuesday night'. Also, don't be afraid to ask other folks if you can tie-in with their plots-in-progress: Interweaving things together that way can help give everyone more reason to be involved.
10: Set a mood. Decide what kind of mood your plot will have.. Is it a desparate struggle until the final triumph? A quiet, but intense trip? An irreverant, offbeat and odd event? A dark, grimy trip into a decaying metropolis? Eventful but upbeat? A 'fantasy epic'? Whatever this mood is, try and set it in the way your NPCs talk, and in the way you present opening and closing poses for logs, and in the language you use for presenting the things and places the characters see.