Whenever you can place archers strategically around the perimeter of the village as they'll fire at anything that gets too close.
Daily reward
Change the date in your phone and start the game get your reward stop the game change the date again in your phone and start the game again and get your reward and so on and on.
Heal
A perfectly legitimate strategy during battle although not a brave one is to run away and let your minions take a beating if you need to heal up.
Special Powers
Don't worry too much about conserving your special powers as they have short cool down times and recharge quickly.