Use the shotgun with the double barrel shot, then quickly take the L23 Fareye and shoot the head. This works best against tall targets.
Shoot a Chimera in the crotch to deal extra damage.
When going after Crawler Pods, put one Sapper Mine in the middle of the pods. Use the alternate fire on the gun and it will blow most, if not all, of them up.
To kill Cray Jacks, use the shotgun.
To kill Hardfangs, use grenades.
To kill Howlers, the shotgun works well, but circle around them because it takes a few shots to kill them.
To kill Hybrids (and Advanced Hybrids), shoot off the tubes coming from the cooling unit on their back and into their arms. This may be difficult, but they die much quicker this way.
To kill Leapers and Rollers, shoot at them with the Arc Charger, then use its Ion Burst.
To kill Menials, hit them with your gun. This will kill them quickly and you do not have to waste bullets.
To kill Slip Skulls, use the Bullseye Tag and hit them. After that, keep shooting.
To kill Steel Heads, shoot them in the head a few times.
To kill Titans, tag them on the head with the Bullseye and keep shooting.
To kill Titans easily, get behind it. Take out your shotgun and shoot at the wires on its back. When you are behind it, it cannot see you. You can kill it without getting hurt.
To kill Widowmakers, tag them with the Bullseye, then find some cover and just keep shooting.
To kill Angels, use the same strategy as with the Widowmaker, but you must keep moving because they throw a spear-like weapon at you that creates harmful gas.