i know the mistakes..
1st- doing ONLY abs/biceps/forearms EVERYDAY! as i did for afew months
2nd- Undereatting -really hindered my progress
3rd-not doing Back/Legs and or Tris/Shouders(amazing!)
4th- coming into the gym 3 days a week for some half assed work out then not coming back in for days.
I would have to agree with the no leg training mistake. I fell under this category, and realized how unproportional my legs (mostly just calves) were to my upper body. Now Im busting my ass to make up for a couple years of stupidity.