The familiar imperative is the subjunctive only if negative. Positive: escribe, negative: no escribas. Positive: Hazlo!, negative: No lo hagas! I can remember the day I learned this. My teacher was Peruvian. I asked her "what's changing it?" and she had to think a long time. Finally she said "it's the no". Look in a dictionary under conjugation for any verb. There are two entries for familiar imperative, negative and positive.
You have subjuctivitis ;-) Search for Besame Mucho on Youtube. Maybe you will have heard it before so that it won't be too hard to learn. That will give you two common cases: "kiss me" and "as if it were". The difference between formal and informal imperative is overblown. Natives will use the informal more often than they admit. So "No tengas miedo".