Now I know I'm still a green-poster, but to address the issue Mr. STARDU5T is talking about with people losing interest or fading out: that's unfortunately human nature. Something can look real cool for a while, but then you move on to something else You might come back to the last thing later, but you might completely lose interest in it for a long stretch of time.
Now, I know I've roughly the equivalent mileage of a wet colt when it comes to seniority here, but from what I've observed in my little time of combing the threads here (I'd do it more often, but I like combing the Round Table section of the forum an awful lot, too) it seems that the OOC tends to exhibit tell-tale signs of degradation a short time before the IC sees post reduction. What I mean is that eventually it trickles down to the OOC being used mainly for post alerts and then more and more for notifications on incoming late posts until those posts just stop coming. Now, I ain't no psychologist, sociologist, or personologist (that last one wouldn't matter too much anyway), but I think what happens--especially when the players don't interact frequently--is that the player becomes disconnected from their character as their attention is drawn toward newer RPs or just other pursuits outside the forum because their character becomes more and more reactive while the thread becomes less and less active. Pre-planning can dispel some of the magic of certain things, but discussion of possible milestones to be reached doesn't constitute pre-planning, it only keeps the players thinking about their character's futures, which gets them more invested, and makes them feel more connected.
I suppose there's probably no surefire way to keep an RP alive, but I think the best way to improve your chances in to encourage the players to talk about what they might be looking forward to in the OOC, or to talk about goals for their characters (goals that might never be reached, but goals nonetheless), and to continue to do so even after they've made their post in the IC so that they remain invested in the world. When no one talks about that stuff, the RP loses a lot of its shine and it becomes more and more evident that it's just a collaborative forum variant of Simon Says in mission-based, or a cheap text version of modded Minecraft in sandbox ones. When one of us reads the OP for a new RP, we're taken with the world the GM sets up because we think of all the possibilities we can pursue there. Once the RP picks up, the GM and the players both have to make sure that magic doesn't fade and that everyone remembers those possibilities they saw when they first signed up.
Buuuut, I probably don't know pudding from primordium, so I could be way out of sorts there.
Also, Mr. Michelaar, for one of the more-qualified persons to give you a specific RP that's accepting, perchance you could share some of what you like? Looking for something strictly Pokemon or something different? You like journey-type deals or closed-sorts ones that have a small environment and a lot of missions?