I am now, have been and will be wrong

good judgment comes from experience
experience comes from bad judgment

Be prepared, but don't do paralysis by analysis. Go out and do. Most of the time you will be wrong. That's OK, it just eliminates the number of wrong things you can do next time.

However, avoid the stupid mistakes, rookie mistakes, the mistakes that everyone else seems to know about and avoid themselves.

This leaves more interesting and valid mistakes to make.

rookie mistake: Running out of cash, not knowing why your customers buy from you, not knowing who your customer is, not knowing the purchasing decision tree of your customers, who signs the checks, what to expect from your suppliers, etc.

not a rookie mistake: A big company all of the sudden having an interest in your area. If a big multi-billion business all of the sudden changes tracks and comes down on you, you lose.