These are more advanced, but have them anyway.
If you get shot first, don't try to fire back because they will still outdamage you before you can kill them. Instead run for cover and pop a medkit if needed.
Now here is the tricky part - they already fired upon you, so they showed on the minimap. Now in ps2 most of the players will try to chase you without a second thought. Look at the minimap and see from which direction they are coming from and then quickly pop out of the cover. They usually sprint so that means that their weapon is lowered. Couple that with ps2 latency and you'll get an easy kill.