1. Everything in source control. Everything.
1.1 Source control on RAID.
1.2 Occasional offsite backups.
2. Get everyone on the same page as far as who's going to do what, and how the parts will talk to each other, before anybody writes a line of code.
3. Never add manpower unless:
3.1 ... they have needed expertise, and no one else can learn it on schedule.
3.2 ... someone else is leaving.
3.3 ... you JUST shipped the last version and have plenty of time to bring the new folks up to speed.
4. (This is a more personal-level tip) No AIM, no IRC, no email while coding.
5. Use Ruby. Or Python, even.