Hi Tim
The accepted SAM defense is to turn to put the missile about 30 to 45 degrees either side of your nose as you nose your plane over slightly and begin a descent to gain speed.
Your game plan is to fly a hard, rolling maneuver into the missile, forcing it to maneuver in more than one plane of motion. The result is that the missile will not be able to pull enough lead to make the intercept.
The problem from your point of view is knowing when to begin the defensive maneuver. In the real world, this will vary depending on the missile type. In the sim world, it all depends on how the sim artificial intelligence (AI)...meaning its program...has the missile behave. This may or may not be 'realistic', and in any case, the AI may have you getting hit no matter what you do. Such is the world of sims!!
The best advice is to practice with your specific sim to learn its peculiarities, using the technique described above. Try beginning the maneuver with a hard pull up (5-7 g's) as you roll moderately hard into the missile. Think of yourself doing an aggressive barrel roll around the target...if you are successful, you probably will pass the missile 180 degrees out. If you see the missile making a large turn towards you as you roll then you may have begun too soon. If you get hit as soon as you begin the maneuver, then you started too late!! Obvious, I know!
Experiment and practice a bit. What you have to do is figure out the sim AI...once you do that, you have a better than even chance.
Andy