Set your guns at 400, then remember where the bullet stream will be hitting at lesser and greater distances.
At 200 it will be higher than the pipper at 600 it will be lower so aim accordingly.
Fire short bursts and change your point of aim till you hit the target.
Fly a P51 till you get it right - good guns, decent amount of ammo and you can evade nme a/c fairly easily.
The drones are a good start - fly in the same direction as them and kill them, then land, rearm and fly in the opposit direction and try to kill them. Try to tag them from the side, top and bottom till you get the hang of it.
Then practice for a couple of years till it's second nature. In five years or so you could be pretty good.