Use upgrades wisely - Use the planet and weapon upgrades wisely on the right items.
Use bombs and mines - Shoot the mines and bombs in the right situations to cause huge chain reactions.
Boss Levels - Concentrate on taking out the little enemies attacking your planet then when you get breathing room lob a volley of shots into the bosses. (full version only).
Planet upgrades - On later harder levels concentrate on build planet regeneration capabilities then planet defense.
Weapon upgrades - Upgrade your weapon first then concentrate on reload then other upgrades afterwards. The more weapon fire you launch over a period of time the more damage you can do. Some weapon upgrades cause very long reload times so be careful mixing weapon upgrades with reload upgrades. In fact we found some weapon upgrades less useful than simply upgrading shot speed.