Questions regarding stop loss

I have read and heard many times that setting stop loss is good habit.

While studying the chart of GAIL, I had observed strong support @ 336, 337 and 339. I did not see any support later on till it reached Rs 260. So I set stop loss for GAIL @ Rs 334. But yesterday on 17-1-2016, GAIL broke all the resistance and went to Rs 330. Stop loss got triggered and all shares were sold @ Rs 334. But surprisingly it bounced back and closed at Rs 336!!

So I think that need to learn a lot about setting stop losses. My questions are: -

1. When to average out and when to set a stop loss? (When market is falling or when sector falling or during bull run etc...)

2. Where to set up a stop loss? In the case of GAIL, I set up a stop loss which was Rs 2 below resistance (i.e. Resistance was at rs 336 and stop loss was at Rs 134). So is it good to set stop loss Rs 10 below resistance i.e. at Rs 326?

3. Should small caps, mid caps and blue chips have different stop losses. E.g. 5-10% stop loss for blue chip, 10-15% stop loss for mid caps while 25-30% for small caps (Or should it be other way round?)

Please share your views.