I eat Reavers for lunch.
They always try to hit you with their rockets and very few Reaver pilots actually know how to lead a moving target with their rockets. Typically I either kill them outright or damage them enough that they run off to repair. If they flee I often chase them the best I can. Sometimes I get lucky and the guy lands nearby to repair. Wait for them to actually get out of the vehicle and then you charge in with the 75mm.
If they actually use the 20mm then I'm in trouble. It's usually a 50/50 match up as to who kills who then.
The best way to get good at it is to practice by actually going after Reavers and Mosquitos aggressively. Keep moving unless they have their back to you. As soon as they turn to fight start moving and keep that 12mm on them as best you can. Most pilots don't actually expect Lightnings to purposely go hunting for them.
Everything I've mentioned is assuming that your Lightning is fully repaired at the moment of encounter, and it is a 1 v 1 face off. We all know that isn't always the case, so take what I'm saying with a grain of salt.
For scarpas -
I'm Vanu/Markov usually. I don't always play the same character or roles when I'm on, but if you do see "gonnagetyou" in a Lightning running around give me a "hey".