I'm incapable of playing something like this without laying out some strategic principles:
When launching, hover the bird at the edge of the atmosphere for a few clicks, to give it time to tilt into horizontal orientation, so your thrust can affect the orbital parameters. If you don't do this, you'll just thrust vertically into the outer barrier.
Circular orbits are best. Two objects in circular orbits at different altitudes can never collide.
High-altitude orbits are best, where there's more room for more objects.
So circular high-altitude is best, but it's not easy to get there. Standard orbital astromechanics apply: to circularize, thrust at apogee to raise your perigee. Problem is, it's not easy to tell when the bird is at apogee, and it may not even occur before you lose control of the bird and the next appears. Also, the thrusting resolution is rather coarse: if the apogee is any higher than about halfway to the edge, two clicks will send the bird into the barrier, so you only get one attempt. These details and coarse controls make the game a lot harder than it looks, just like the original Flappy.
Finally, if you just need that one more point to break your high score, launch the next bird into the lowest fastest orbit possible. That altitude should be clear if you launched all the other birds higher, and it will register quickly before any more collide. I managed 8 thanks to this.
