It's worth going to have a good read around things if you're dropping flares.
The basics are:
- The 120 is a Fox 3, radar guided missile. This means that the aircraft radar normally provides guidance to the missile until 10 seconds before the missile is due to hit the target, at which point the missile goes "pitbull" and turns on it's own radar to track the target
- As the missile is radar guided, flares will have no effect. You should/could be using chaff. Don't drop 1 though. A stick of 10 in a sequence is typically more effective
- The 120, like any A2A missile is fired using it's internal rocket motor. Be aware that they only burn for a few seconds, which accelerates the missile to mach 3 for the 120. Post that burn, the missile is "coasting", and therefore decelerating. You can burn off the energy of the missile (i.e. it's speed) by making the missile make changes to it's course
- Be aware of the range of missiles. The 120 is "approx" 20 miles. However, if you're chasing a target, it's far less and if the target is coming directly towards you, clearly that increases. If firing a missile, being high and fast helps. The other way around, if you're at low level as the target, air density increases, which adds drag and slows missiles even more
- A2A missiles typically try to plot an "intercept" course for their target. As such, they'll be trying to fly to a point in front of your aircraft
- Good defensive tactics includes "notching" (worth looking that up). In rough terms, if you're flying towards the enemy, turn left, meaning that the missile will turn in that direction, then make a hard 180 degree turn. Chances are that the missile won't have the energy to come after you. Notching doesn't need to be just in the horizontal plane. IMO, it's also good to use the vertical plane aswell.
- Radar guided missiles are dependant upon the radar being able to see you. If you're low level, you can use cover (hills) to hide behind, which will break a radar lock
- The F14, F15, F16 and F18 all have bother Range Whilst Scan and Track Whilst Scan mode. In Range Whilst Scan, when a missile is launched, your radar warning receiver will let you know. However, if a player is feeling more sneaky (and good ones will), they'll use TWS. For that mode, you do NOT get a warning when the missile is launched. Instead, you'll get an RWR warning when the missile goes "pitbull", meaning that you've got just 10 seconds to evade. Unsurprisingly, it's a LOT more dangerous.
Once you think that you understand the above, go set yourself up a mission using the editor such that you can keep practising being shot at evading missiles