You have to capture flags & upgrade your own flag. here is a list-
- capture 1 flag - get a bronze flag, remove 3 boulders
- capture 3 flags - get a silver flag, remove 2 more boulders
- capture 10 flags - get a gold flag, remove 5 more boulders, get a radar upgrade
- capture 50 flags - get a platinum flag, remove all of the boulders in your base, get a star on your trainer card.
hope this helped
source - here