I think the best way to get past fear in lucid dreams is just to force yourself to do things that would be dangerous to do while awake. Decide on a few goals,(I suggest jumping from high places, or setting yourself on fire, I've tried both and found that they're both interesting experiences) and as soon as you're certain you're dreaming, make yourself try them immediately. It'll probably be frightening at first, but after enough firsthand experience that you cannot be hurt in dreams, things will be far less likely to be frightening in lucid dreams, and any fear that is left will be easily overcome.