200 Extra Points In Tofu Mode
When you kill a tofu, keep shooting it's peices for more points.
Using any weapon (preferably the linear launcher) destroy random stuff like computers or dressers needlessly. And try to to kill stuff that is difficult to hit like a bunch of monsters outside an elevator while the doors are closing or pretty much any thing you run away from that you wont see again.
Weapons You Should Upgrade First
I found upgrading guns that run out of ammo a little
counter-productive. So I decided to upgrade my regular hand-gun. This is the best possible option because it makes all bosses, zombies and monsters practically ineffective on pretty much any difficulty. Now as far as I know there is
only one other weapon with infinite ammo and that is the linear launcher which I earned by fully completing hard mode in co-op. This weapon helps quite a bit at first but when it is fully upgraded it makes you unreasonably powerful because it makes massive explosions stronger than the rocket launcher with continuous fire and it is recharged before you finish inserting the recharge cartridge.
This makes all other weapons pretty much useless to upgrade or even use. But just because you don't have a reason I did it just for the heck of it. (cuz its kinda cheap and makes you weak).