I'm playing on Commander difficulty, if it matters.
I have some simple plans for fighting each UFO in the early game to delay upgrading my air capability as much as possible because I always feel behind on tech and resources in the ground battles.
Probe - Barrel roll the first shot at the last second, which also dodges the second shot. Get hit by the third shot, roll the fourth, and now the probe is dead to your autocannons.
Scout - Get behind the Scout, then it can't turn as fast as your Angel, which gets free damage until the Scout is dead.
Destroyer - Come in at the side, then hug its side. It cannot turn faster than you can manuever, but you may need come in and out of range sometimes so that you don't run into the destroyer.
Fighter is the first UFO that I realize I can't defeat with Angels and Autocannon, and I'm realizing that lack of alloys and alienium throttles my development at that point in the game. I know that at this point in the game, you *can* have a lot of tech, but I want to know what the bare minimum of tech is so that I can invest minimally in air that stage of the game.