Practice your free throws. Good free throw shooting teams win games in the fourth quarter. Thus prolonging your life. Sniping enemies will conserve your health and ammo if you are able to take them out with a head shot. Combine this with the crouching feature and you will lessen the chance of being detected, making it easier to take out your target with as little mess as possible.
Different weapons work better on different enemies.
For example the war blade is an excellent weapon to use against the smaller enemies, spiders and bees. While heavy fire power, the scorpion launcher or grenades, will be need against the Soldiers in the hive. However, the Shredder is a good all around weapon able to handle any enemy. Learning to aim is an important task. Shot placement does count.