I rented the game, so it didn't have the manual. Is there a trick to avoid the missiles, or I just run away?

Think u need to find sumwhere else to rent ur stuff from as u shud at least get a photocopy of the manual!
Theres no real secret to avoiding them nuffin in the manu al as far as i know(never had manual)
Best way to avoid them i found is to get pretty high and wait till the missile is pretty close then drop fast and move either left or right! about 80% of the time the missile will miss u!!

p.s. Tip: When ur getting attacked by SAM sites then try and duck and dive using the scenery and try to find the radar station!! Take out the radar station and the missile will not operate/fire at u!! Saves missiles etc

One way to do it is to hide behind stuff. For instance on the first Alaska mission you have to attack the base you flew over. There is a mountain side you can get behind near the north east corner of the base. Get behind it at a low altitude. Then pop up,shoot a missile and duck back down.

Thank you for your insights

When a missile is coming a beeping noise can be heard. The faster the beeping the closer the missile.

Radical changes in altitude just befor missile impact generally does the trick. Usually any maneuver that is faster than the missile can turn will work.

Or just generally moveing out of the way tends to work.

The best way I found to avoid missiles is to go straight at it, while moving up or down, and side to side. If you fly away the missile will probably hit you (It's much easier for the missile to hit something going the same direction as it). I've also learned to lock on to a radar from behind mountains, then turn and fire your missile around the mountain. The missile will turn and find it's target.

Thats because helicopters move faster forward than any other direction so your tip only reinforces moving rapidly. Like what I said. Also think before you move into an area and plan your attack helps remarkably.