Complete the game on Veteran. This is really easy in comparison to Call Of Duty 4. You can get shot many times and still live. The only thing you do not want to do is get cornered. Being cornered will mean yopu die instantly, there is pretty much no way out... Take it slow and reload often. Pick up enemy weapons often for ammunition.

Also remember: Stealth missions aren't meant for you to be detected. If they find you, it will be a LOT harder. If you aren't going to restart at the last checkpoint, try to flank your enemies and watch your back. Team mates are terrible at protecting you. You need to stay in cover. But remember that wooden covers aren't the best because enemies can shoot right through it.

Watch out for shotguns because the enemies have many of them and can ambush you. STAY IN COVER, this isn't Call Of Duty WaW with infinite grenades. The enemies only throw one or two grenades at most. Helicopters can also be killed with normal guns, keep that in mind! It only takes half or so of a Light Machine Gun and a couple of clips of a Assault Rifle/SMG.