Legionary - This is the most common foot-soldier you'll face when fighting the Cabal. Watch out for the jumping ability that can bring these guys into close range quickly, and try to hit them in the head for extra damage.
Phalanx - The Phalanx fight much like the Legionary, but they have a shield instead of a jetpack. Try to shoot an exposed part of this enemy's body, or flank it if you're struggling to get a clear shot off.
Centurion - The Centurion is best described as a hybrid version of the first two Cabal enemy types. Use Solar damage to obliterate their shields, then finish them off fast - if they get into cover they'll heal themselves quickly.
Colossus - These slow enemies pack deadly melee and long-range damage, but you should be able to dodge the worst of its attacks. To take them out, try to deliver as many precision headshots as you can from distance.
Psion - The Psion is a quick-moving creature that can fire waves of deadly energy damage your way. Jump out of the way of these attacks whenever possible, and aim for the head when returning fire.
Harvester - The Cabal's drop ship can appear anywhere on Mars, and its generally a good idea to simply keep your distance from its Solar turrets.