Running into battle with your guns blazing doesn't always work.
Figure out your enemy, and deploy the best tactics in defeating them.
Take cover if you're taking too much damage, it will save your life.
Take this time to reload your guns, and get back out there as soon as possible.
Your enemy takes time to recover too. Don't give them this chance.
Use your bow and knife whenever possible to conserve your ammunition with your more powerful guns.
Use the flares from the shotgun (assuming you have it) to give Raptors a different target.
Every enemy has a weakness. Find it, and use it.