Here are some tips when getting started on the Campaign mode of Call of Duty 2.
Obey your captain
Your captain or squad leader knows the battlefield and where the enemy troops are, which is why you'll often see him with his binoculars out instead of fighting like everyone else. If your leader gives a command then follow it, as it is the best way to complete the objective. Even if in your eyes it looks like a suicidal action.
Read the diary entries
On the loading screen before each mission they'll be a diary entry from you. This explains what the main objective is and what strategies the Germans are using overall. It's worth reading this to a little bit extra information before going into battle. Some missions really do start of with a bang and so the info helps.
Use smoke grenades
If there are certain areas that you can't seem to get past then throw a smoke grenade and it should allow you to move forward. Use them sparingly though because you only ever have four at a time. In some missions, especially on Veteran difficulty, it's pretty much impossible to advance forward without using smoke.
Crouching and proning
You should nearly always be crouching. Crouching allows you to hide behind obstacles better and it's harder for the enemy to hit you. The disadvantage is that it's slower to move. Unless you need to run across an area quickly, or you need extra height to look over something, always crouch.
Proning is great for hiding round a corner and then edging your way forward around the corner where you know enemy troops are. Be ready to get up and run if you see a grenade as it's unlikely you'll avoid it if you keep crawling. It's also not ideal when outside as there is often long grass and so there is no clear view when crawling.
Methods of clearing out the second floor
One of the hardest bits of the game is when you know there are enemy troops in the second floor of a building, but you have to go up stairs to get to them. What you should do is try to see what possible routes there are into other rooms. If there is just one route once you've climbed the stairs then it's pretty easy, but if there's two then it's hard because if you get to the top of the stairs they'll be enemy soldiers shooting you from two directions.
Try running up and down the stairs until you know roughly the positions of the soldiers. Then try and slightly move forward until you see an enemy and fire, then quickly run back down the stairs. Continue doing that until all soldiers are dead.
You could alternatively chuck a smoke grenade so that it blocks off one one side of the landing and then you can take out soldiers on the other side; or you could simply crouch forward and use melee attacks whenever the enemy gets near.
Another effective way to move up stairs is to put your back to the wall and move up sideways by pressingor . This lets you keep your attention upwards and to the open part of the stairwell. If there is a landing or balcony above that lets enemies shoot you in the back as you come up the stairs, try backing up the stairs using while watching the landing for enemies.