Here's how I did it:
RING RACE - Forget about being fast. Choose a light plane as they are smaller and fit in the rings better. Go through the level as slowly as possible so you get points for < 3 rings hit. Just hit X whenever you are close to a ring. If you find it difficult to maneuver through the rings while turning, try to adjust your position so that the next ring is in the middle of the screen. It doesn't matter where your plane is, if the ring is in the center of the screen, you will go through it. Take your time. Do a scout run first if you want so you know where the rings spawn.
FOLLOW THE LEADER - I used a Light plane. This mode is very forgiving. You can get off track many times and miss some of the stunts, and still get 3 gold medals. Focus on trying to stay at the proper distance. You don't have to be "in the smoke". It's all about the distance you are from Charlie Brown. If you get off track, use your turbo to catch up and don't lose hope. You can still get the 3 medals. You do want to focus on doing most of the acrobatics when prompted as you get more points for that. Learn the route too,
BIRDS OF WAR - Choose a Heavy plane so you can absorb the hits from the bombs. Figure out the best/shortest route to go from one Bird to the other, so you can get the Time bonus. I discovered that if you hit the Turbo button 3-4 times per second instead of holding it down, you will go faster. Use this to get the Time Bonus, which is what you need to get all stars. Forget about the Damage. You will get hit more than 3 times, but if you get all the other objectives, you will get the 3 medals.
You can check the criteria for getting 3 gold medals in-game by pressing Start and then Objectives.