Here's some things that might help you out - Make sure you upgrade your melee a couple notches, it helps. Make your shots count, use enviroment to your advantage, like explosive barrels, traps etc.
If youre fighting a couple zombies at once, a good trick is to down the closest one to you so he falls on the ground, then if the others are close to him, throw a match on him and you can light a bunch of them on fire. Try to group them up for grenades or by an explosive barrel.
Make sure you explore because theres lots to find out there, like green gel to upgrade Sebastian, ammo, weapons etc.
Shoot the little white statues of Mother Mary(I think its her) that you see around the game, sometimes they drop keys that you can use to get stuff in your safe-ward.
I got a good laugh out of video on youtube in the worth a buy channel as i agreed with it, this game disappointed me big time.