HGTV's has a list of the "Six Deadly Sins of DIY Projects" that really touched a nerve with me. I have to admit my greatest weakness is tackling too many projects without comprehending how much time each one is going to take. They are:
Time. Too many projects, all at once
Money. "Almost impossible to foresee all the costs"
Skill. If you pretend to be an expert, you will fool no one
Planning. More planning usually means smoother renovations
Mess. I have yet to be on a job site that doesn't resemble a complete disaster area
Enjoyment. You should remember that there will be good days and bad days
I'm writing these down and posting them on my toolbox.