Interesting game. Really hard untill you figure out a few things.
1: Take your time. Sweep the perimiter of the stage of small stuff and hope for some better spawns as you sweep around again.
2: gravity is your 'sensor' as that slight tug will tell you theres a threat nearby.
3 Gravity is also how you lure planets away from larger threatening ones by getting just close enough to drag them to you.
4: Gravity is also how you tell if a simmilar sized planet can be absorbed. If it moves towards you, Then its probably good. If it doesnt budge or you move towards it. Then bad.