To get that Best 3000 medal, first grind until you've unlocked the final ship.
As the final ship, fly between the first two grey asteroids. Then, and this is very important, fly under all the red asteroids, almost going off the bottom of the screen. In fact you'll have a few pixels leeway and might die a few times but can get the hang of it. Do so until you have a score of at least 3000. You'll also notice this gives you many more points than flying in the middle. (Which you couldn't do anyway due to you'd die due to terrible game design)
Only way the ridiculous scores in the game are possible.
Most of the rest of the medals in the game are just grind.
That leaves the 1000 points with the first ship medal, which is possible. Note it isn't possible to get very far with any of the later ships (unless you're dipping beneath the lowest asteroids) and this dipping beneath trick isn't possible with the first ship.