I am a F2P player. It's been a month since I started playing and I am at level 65 and about 17k power. Also I have collected about 3500 coupons.
I was wondering that I should start spending the coupons as I have not used a single one till date. So how should I spend them most effectively?
I am told that I should be spending them on the power items. But since I am not that aware about various features that are in the game or that are about to come, I need a suggestion on this context.

Thank you in advance.