A nice list of developer mantras:

http://www.pragprog.com/the-pragmatic-programmer/extracts/tips

Excerpt:

• Don’t Repeat Yourself
• Eliminate Effects Between Unrelated Things
• Don’t Assume It - Prove It
• Design with Contracts
• Finish What You Start
• Refactor Early, Refactor Often
• Test Your Software, or Your Users Will
• Don’t Think Outside the Box - Find the Box
• Coding Ain’t Done ‘Til All the Tests Run
• There Are No Final Decisions
• Fix the Problem, Not the Blame
• Crash Early
• Minimize Coupling Between Modules
• Don’t Program by Coincidence
• Start When You’re Ready
• Find Bugs Once
• and many more …

If you want to find out more, check out the books at the bottom of the mentioned URL.