This will keep you well-stocked for future battles. Once in awhile, enemies will drop special goodies like double weapons. Know your weapons. Memorize which guns have small clips and which have slow rates of reload. Keep in mind the secondary function of each weapon as well.
Some weapons are twice as effective on their second setting.
Go for headshots if you can get them. One-hit kills save ammo. Don't get addicted to them, though. Trying to line up a headshot in heavy combat is like trying to knit a pair of socks on a roller coaster. Lure your enemies into more advantageous parts of the arena.