Not my idea, but a great topic for discussion.
I'll post them without explanation and we can get into some discussion later.
1/ Not understanding the independant effects of time and volatility on your option.
2/ Only ever using one strategy (e.g. covered calls)
3/ Not understanding the proper use of leverage available
4/ Not understanding the fundamentals of option pricing theory (the greeks , synthetics, black scholes et al)
5/ Thinking the expensiveness of an option is determined by the dollar cost of the option
6/ Using complicated strategies when simple will achieve the same goal.
7/ Not knowing how to pick the correct option for the selected strategy.