Nice list, and I agree with everything you all have added!
Planning is the biggest one of all! Look at everything from every aspect possible, and then ask others to look at it as well. It's extremely important that you consider everything before jumping into things, and it goes so much smoother!
Also, some young entrepreneurs tend to have an unrealistic mindset (I can sell 4000 of this product in my first week!). Make sure you know what you're getting into, and don't expect something that won't ever happen.
Writing is a socially acceptable form of schizophrenia. ~E.L. Doctorow