When a pirate gets an upgraded weapon, they will unlock abilities. These abilities can be used once per level. For example, the barrel pirate will be able to place three barrels in random locations, allowing you to clear out a large space quickly.
Wait until your pirates stop moving before you aiming and shooting. If your pirate loses his footing, wait until he has completely stopped again before trying to fire.
One your starting pirates can throw barrels. After throwing a barrel, there is a short amount of time that you can tap again to explode it. It does enough damage to remove obstacles and debris. If you do not tap to explode it, the barrel will remain in place. If it gets hit by anything else with enough force, it will then explode.
Earn a gold skull on a level to get gemstones. They are used to upgrade pirates.
Shoot crates when they appear to get a chance to find a key. Keys are used to open silver chests.