Instructions
Keep moving forward. The level design employed in the "Call of Duty" series tend to avoid large open areas where the player may get lost. When in doubt, keep going straight.
Aim for the head when shooting the enemy. The largest obstacle in your way in any given "Call of Duty" game is the never-ending supply of enemy soldiers which press you at every turn. Head shots are the quickest way to ensure that the S.S. officer you just shot is not going to get back up.
Take cover often. When playing on the higher difficulty settings in the "Call of Duty" series, it only takes a few well-placed shots to bring you down. Taking cover allows you to regenerate health.
Complete listed objectives. The goal of any given mission will be different than the last. Some will require that you fight through enemies, others will call on you to blow up German rockets. Paying attention to the objectives listed on-screen will keep you on the right track.
Pick up enemy weaponry when low on ammo. Enemy weapons kill bad guys just as well as the weapons you start with and ammo tends to be plentiful since the level is filled with bad guys.
Do not die. Dying in a mission leads to an automatic failure.