Tip 1
If you have zero intent of investing any real-life cash on this game, head over to the in-app purchase shop even. Among the added alternatives is to watch advertisements and get presents. Presents will usually consist of such goodies as free stars. The free presents reload after 3 hours, and while you cannot time cheat them, you can set push alerts in order to gather them as quickly as they prepare.
Tip 2
Return through each level to care for all your objectives for additional bonuses. It's almost difficult to care for each and every single objective at the same time, however, so return through and take on one objective at a time per play-through. Just ensure to endure to the end due to the fact that if you do not beat in charge, you will not be credited with finishing the objective, no matter just how much of it you completed.
Tip 3
Attack tanks as quickly as you see them if you are running a bit low on life. The majority of them will spit out hearts, when you get a heart, a few of your health is brought back. If you restore your health to complete then complete the level without losing anymore health, you will be credited with the "remain unblemished" objective.
Tip 4
Early on in the very first level, and in future levels after you unlock them, concentrate on shooting down as lots of ships as possible and gathering the stars that fall out, however after a weapon upgrade or 2, concentrate on durability and the stars will care for themselves. Concentrate on preventing getting shot above all else in order to get as far as you potentially can. Kill the boss and you can open up the next level.
Tip 5
In addition to picking up stars, gather all the shooting rate upgrades (the little silver diamonds) that you see. Every one enhances the shooting rate by just a bit, however pick up a lot of them and you will wind up building up a big shooting rate upgrade by the end of the level, which assists enormously when attempting to kill harder enemies or various and large rows of aircrafts.