I've run several successful PBPs and several unsuccessful ones. (It's been a very long time since I did PBEM.) This is based on my own experiences only.

Have good infrastructure

I usually set up a phpBB-based forum solely for use with the PBP, rather than using an area of someone else's forum. It makes it much easier for me to administer and tweak.

I set up custom ranks for each player to indicate which character he or she is playing, which makes it easier for the players and myself to keep things straight. I encourage avatar use as well.

Another advantage of having your own forum is that you can easily set up "private" forums, each of which only a given player can see. This is useful for "note passing," keeping track of xp and private conversations, and so on without having to go through a backlog of PMs.

I usually have an out-of-character forum for intros, general discussion, and metagame stuff, and an in-character forum for actual play. I devote a separate thread to each "delve," as I'm currently running an OD&D campaign.

Be active, have active players, and communicate interruptions

The paramount concern in PBP, in my experience, is having active players. I ask for some kind of substantive post at least once a day. Stagnation is doom in the PBP realm — once things slow down, heat death follows. If I can't post for a few days — which happens — I let everyone know, and expect the same.

Start the game with clear direction

One thing I discovered running a City State of the Invincible Overlord PBP a couple years back is that too many options at the beginning of play can lead to decision paralysis as the players try to decide what to do. In a dungeon-type game, I'd recommended starting at the adventure site, getting stuck in, then getting to the roleplaying after the players have the swing of things. In a story-type game, I'd consider starting in media res, like with a chase scene or something that gets the players thinking in-character quickly.

Pace your background exposition

Finally, I'd avoid excessive infodump. It's great for you, as the referee, to know lots about your setting, but I'd keep the early background to just enough to give the players a sense of things and parcel the rest out through play.

• 4e works quite well over Google Wave. The RPG-Bones applet has a very acceptable interface for a battlemap.

• Trust your players. Don't worry about cheating. Just agree on what level of die roll honesty the group wants at the start of the game. My preference is: "You may always choose to fail any roll" but some groups may choose to play "just call them as you see them" or even "Anyone can fudge any roll." Adding technology adds complexity, and there's always a way to cheat, so don't worry about it.

• Be very clear on what the group's goals are. Do they want a tactical challenge? Do they want to share a story? In my game we have ended up toggling between combat encounters then a bit of narrative and then a bit of combat. Make sure you work this out with your group

• Figure out what to do about "timeouts" How long each player has to submit their turn, be it narrative or tactical. What happens when they don't?

• The DM must assume competency: if the player states something and there are multiple ways to achieve it, the DM must choose the most optimal way for the player.

• Explore batching: agree on when rolls are needed. If possible, let rolls ride (one roll to determine the use of the skill for at least the encounter). If at all possible, try to get batches of rolls that can be adjudicated in parallel.

• Agree on amount of shared control: can players determine scenery? Can players put words into other's mouths? The more shared control, the faster the game, but some people don't like to give it up. Try to have each player provide guidelines for writing their character. Voice, types of actions, taboo, etc.

In general, it's probably worth your while looking at our wave game (combined with the chat logs in The Back Room) For that matter, I'm happy to lead a group character creation (that worked incredibly well for my game) for your group.