If you want help with getting past a level, post it ere. I won't tell you exactly how to do it (that would ruin it anyways!) I'll just give hints.

for example, level 19: Many people have trouble with that one. Here's a hint: Bombs, bombs, bombs! Also, the enemies are extremely predictable while in formation; kill 'em while they're easy to hit.

I've become quite the pro at this game and can get through the whole game 3 or 4 times over without losing my first plane and have a high score of over 9 million so if you want some great tips print this. I'm not trying to brag, I'm just hoping someone can elaborate on my tips so I can get higher than 9 million.
Level 1: It's pretty easy
Level 2: Easy. Kill the planes kill the balloon. Fly straight up and let the planes follow you to hit with bombs.
Level3: Don't start the level shooting at all. Get in front of the planes and bit higher and poop out the bombs on top of them.
Level 4: Bombers. Start the level shooting and flying straight until the fighters appear. Kill the two fighters.You can rack up huge points by shooting the bombers until they puff black smoke then get way behind them and riddle them with bullets all the way to the ground.
Level5: Angle upwards and strafe the the oncoming fighters with bombs. What few are left just kill. This level is pretty easy.
Level 6: Fly the opposite direction the plane is pointing when the level starts by looping up and back. Fly all the way to the left until you can't go any further. The enemy fighters, for some reason, won't shoot you over there and they love to follow you up where you can drop bombs on them easily.
LEVEL7: Nothing special here just kill the planes and targets.
LEVEL8: Immediately double back without engaging enemies and fly as far to the left as you can. The planes won't shoot you back there just like on Level 5.Sometimes they will fly back to the right so you have to go after them. They WILL shoot at you over there.
Level9 This bomber level can be hard. Start out NOT shooting and fly over the first fighter cruising behind the bomber. If you don't shoot, it won't move. When you get over and in front of it poop out 2 quick bombs and kill it. Then go back to the left and wait for the rest. Kill them and score big points slaying the bombers.
Level 10: The air ship is real easy.
Level 11: The bombing run level is easy. Just go forward at a low level and bomb the ground targets. The only fighter will follow you up so you can drop a bomb on it. finish of the other ground targets.
Level 12: The Barrage balloon level is easy.
Level 13: The Ace pilot. To beat this every time just go forward and kill the ground targets. After the last target go straight up. The ace pilot will be following. Drop 2 bombs to kill it. You MUST shoot the parachute afterwards.
Level14: The convoy is easy. Make sure you take out the first two vehicles at the head of the convoy FIRST. Then kill the rest.
Level15: This level gives you lots of bombs. Fly straight and get a couple shots into the balloon before doubling back. Strafe oncoming planes from above with about 10 bombs. Clean up the survivors. MAKE SURE you save enough bombs to finish off the buildings.
LEVEL 16: Gun jam level. As the planes approach strafe the hell out of them with bombs from above(of course).. I've actually killed them all in one pass a few times. You only have a few
bullets in your machine gun. Use them after the first pass. Then strategically drop bombs on the remaining few.
Level:17Death from above. Easy. Double back and drop bombs 2 at a time on the bombers. Fly as close as you can over them. Keep an eye out to MAKE SURE the bombers are dying. IF one doesn't immediately go back and kill it. DO NOT fly under the bombers as they too drop bombs.
When you get to the end of the screen(all the way left) you are in La La land where the fighters will not shoot at you. Take your time and score big points dropping bombs on the fighters and killing the parachutes.
Level 18:Break the line. Sooo easy. Immediately double back to the far left of the screen. This is LaLa land again where the fighters will not shoot back and you have 24 bombs. take your time and mop up points killing with bombs and shooting the parachutes. BIG points level here.
Finish off ground targets as you escape to the right.
Level 19: The dreaded Ace escort level. It's not that bad. Ignore the ground targets. It starts you off flying over your 4 bombers you must protect. Come in flying in between them. Two bombers above you, two below. as the first group of fighters come at you strafe them with 5 or 6 bombs
and keep going. As the next group comes do the same. If you did the job well there won't be too hellatious of a fight. Kill the ACE pilots FIRST. I often get through this with all 4 bombers left.
Level 20: Short supply is easy. Immediately double back to the far left of the screen till you can't go any further. This is LaLa land again where the fighters won't shoot back at you. Kill them with machine gun ONLY. You'll need all your bombs to finish off the buildings or shoot the balloons to crash into the buildings to save bombs. DO NOT run out of bombs with a building standing or you lose.
Level 21: Do not fire your machine guns as you approach the first bomber. Fly over it and drop 2 bombs to kill it then fly straight up and let both fighter planes follow you up (hopefully)as you unload bombs on them. Hopefully you got them both. Bomb the bombers.
Level 22: Fly up NOT into the cloud(the enemy will double back) and drop bombs then head way way to the far left of the screen until you pass your reinforcements. Just hang around there while they battle it out then head back to the fight and kill them.
Level 23. As the planes come make sure you hit the Ace with bombs. Make sure you get the parachute or you lose.
Level 24: See level 17. Same strategy.
Of course I didn't mention you want to kill as many parachutes as you can along the way if
you want big points. The ONLY way to get huge points is to get through the WHOLE game without
EVER dying.
This is my basic strategy. Hope it helps!