My first DnD game and the only game I'm currently running (technically). While I've only run three full adventures over eleven sessions or so, I think it's been a success. I attribute much of that to two factors: frequent play and minimalism.
Frequent play does a lot to keep momentum up. Players remember facts and characters. They stay energized and anticipate playing. I picked up a regular schedule (mostly), which keeps me pushing forward on stories and gives players time to get their own affairs in order for play. Especially for me, learning a new system, it keeps the rules fresh in my mind and running the same adventure over and over again helps. Even better, I'm running on a six adventure timer. I don't have to worry about Adventure 7 or 10; I don't have time. If I there's villain in Adventure 2, he's going to have to show up again by Adventure 6 or not at all. There's aren't--and can't be--a lot of interwoven plot threads where X affects Y because it's just six sessions and I don't have time for that bullshit. Sure, there are vague ideas about the second arc, assuming the first ends well, but I'm simply refusing to think of it until I'm done with this one. I'm focusing on, maximum, six stories at a time, usually self-contained. I've found it very liberating, which brings me to my next point.
Freedom is Slavery
I've long been a proponent of minimalism. When I play Battletech, I like my full-on, thousands-of-construction options Technical Manual. However, I also appreciate minimalism. Simple, Succession Wars technology that consists of one engine type, one armor type, one structure type, only one type of heat sink, cockpit, actuator, or gyro. Weapons? Eighteen or so weapons. Even given those very simple tools, you can create a variety of diverse war machines with character and style that no teched-out monstrosity created from cobbled-together junk could compare to. When I started The Ciaren Campaign, I limited the players to just the 4th Edition Player's Handbook. The main reasons behind it were split between the versatility of simplicity and my own unfamiliarity with the system. The decision incidentally prevented players from leveraging rules from sources I didn't have access to, and cut down reference materials to a single tome.
In addition, the forward moving story structure kept me from having to develop any single place in depth. I could create one-note villages without having to consider too deeply the implications of such or if I would have to revisit it. The heroes discover new towns and locales to keep them entertained, relying on quiet moments during adventures to serve as opportunities for characterization. Indeed, each character is from their own mini-state inside of Ciaren that they can simply ad-lib into creation at will. I don't have anything on their home towns but what they've given me, and while I would like some more mention of that, I can't really say that it hasn't been working so far.
You Know What You Doing
Skipping the use of Experience has also been helpful. While it doesn't let me acknowledge players who are doing a good job, level players every adventure is great practice with the 4th Edition leveling systems, without slowing any of my players down with math or worrying if someone is adding correctly. Similarly, I've eliminated loot drops from dead foes and purchasing items from cities. Not only does the setting not have any major cities, but the trade of items (especially magical items) isn't something I want to be a part of the game I'm running. I know that I've added Wizard conscription as a game element, but I'll be the first to admit that prohibiting the purchase of magical items on that basis is purely a judgment call. That said, trading, bartering, and gold are no object in the story. The characters have their 'heirloom' items and as they learn to unlock their secrets, those items become more powerful, meaning that I'm allowing them to buy levels of magical items equal to their level times two. As they level up, they learn more about their equipment. Aside from that, there isn't much in the way of equipment that they need as they level up. No one suddenly needs a climbing kit at Level Eight or anything. It hurts the versimilitude when haggling at the bar or earning free drinks doesn't mean anything, but once I get over that, it gives the players far more opportunities for spontaneous roleplaying instead of verbally jostling NPCs until a shiny thing falls out of them.
Simplify, Simplify, Simple Fly
Something else I'd attribute the current success of The Ciaren Campaign to is simple stories. rolepaying games run long, and I'm just now getting to the point where I'm willing to put stories into a setup, pursuit, engagement, and denoument fast track. I think sometimes I used to make things more clever or more vague than I had to be. I really didn't stop to look at what I was planning and ask myself, "How long, in real life, will it take them to do this thing?" A vital and obvious question, but, sadly, only a recent one. I've also learned that despite all of my protestations to the contrary, combat really did take up a lot of time and I did it often. I think that it was in some part due to my presumption that my players wanted to fight, but it was also due to the fact that a fight was a satifying type of conflict or resolution for a story. "They fight on, and MacDuff kills MacBeth." will eat up a lot of your runtime, but it doesn't necessarily make for a good story (Also, spoiler alert). Working to make fights minimal and short has helped immensely. Luckily, DnD 4th Edition's combat has become dramatically easier and more intuitive to use just as my tolerance for dragging, reference-filled combat in roleplaying games has fallen off. Sharply.