You are rewarded with a loyalty bonus for each day you log in. This is one method to earn badges, besides completing Boss missions. Badges are used to purchase better card packs.
Running
Tap and hold to have your character run. This is useful if you need to quickly reach a supply drop. Be careful not to accidentally attack while running.
Side indicators
Some difficult enemies can switch sides after getting damaged. The bars above their heads will signify this. When it is blue, they will be on the left, while red indicates that they will be on the right. At times they will not try to switch sides, and instead just have multiple hits.
Weapons
If you have a weapon equipped, your attack range will increase. Consider your remaining ammunition and make sure you do not tap more than necessary to avoid misses.