I'm going to be a little redundant here, but my observations on gaming groups, having run/played in extremely consistent groups, and very inconsistent groups over the last 5 years.
A major factor in picking your players has to be reliability and commitment. Make it clear that people are expected not to constantly miss sessions. Also, seek players who have at least somewhat flexible schedules so that if circumstances change slightly the game doesn't fall apart. Finally, if you have a player who is going through life changing events (new job, having a kid, getting married, etc), spend a few minutes getting to open up on how realistic it is they will be able to make sessions under their new circumstances.
Start your group smaller, 4 players, and then once you are convinced these guys are reliable add them through referall. Avoid adding people who have mentioned 'that might be interesting' or 'I haven't played in 20 years but I'd give it a shot', unless you don't mind them leaving.
Encourage interaction via email or a website between sessions. Not everyone will necessarily follow these emails or discussions as closely as you like, but it keeps people engaged in the game between sessions.
Avoid 'big story' plans that rely on the players. Set various plots and characters in motion in the world and then see how your PCs get drawn into those plots. The worst thing you can do is, for example, give every character part of an interlocking prophecy that will come to fruition 12 levels from now. When people quit this throws your 'master story' off. As your group progresses a good DM can drop enough vague plot hints that he can weave them together into a 'big story' later in the campaign, and the players won't even realize that he didn't actually know what that 'big story' would be at the start.
In short: Stress finding reliable, flexible players. Avoid long, complex plots that rely on one key player to make sense.