Jumping before initiating a heavy attack almost always works for me, but with more success with the alien's focus ability than the predator's. Though you could say it's a noob tactic.
Hiding out in a narrow corridor with a shotgun works against predators most of the time.
I would advise using the smartgun or a grenade against a pack of enemies fighting each other.
Most players nowadays will opt for heavy attacks, so LA or melee them as soon as they come into range.
On a note, you will most frequently encounter in the refinery map predators looming all over the second floor, and aliens in the shadows or on the ceiling on the first floor.