Combine the Sapper's trap and the Green Beret's decoy, this way you can get rid of whole enemy patrols. Just put them down in the right postions and voilą, you can get rid of them one after anonther.

Try to get as far as possible in a mission without setting off the alarm, you will have to fight against less enemies.

Your Marine (Diver) can carry two other commandos in his backpack. It means a safer way of transportation, as the Diver cannot be seen while diving. On the other hand, it also could mean if the Diver dies, two of his buddies die with him. But I never experienced the death of a Diver with two buddies in his backpack so that's speculation.

Before each mission, spend some time looking over the map and note any patrols or guards that might cause you trouble. Note anything that might get in you way!  

Learn the hotkeys! Learn all the hotkeys for each commando. Hotkeys make everything so much more faster and so much easier. Here they are:

Keys What they do.
A Explode remote bomb (Sapper)
B Release bomb (Sapper)
C Crouch/ Lie down on the ground (All exept the Spy when he's in a uniform)
D Diving Gear (Marine) or Distract enemy (Spy)
E Grenade (Sapper)
F Shovel/ Dig yourself into snow (Green Beret)
G Your gun ( Wesson & Smith 9mm Pistol)
H Hand (used for picking up items)
I Activate / Deactivate acoustic decoy (Green Beret)
J Trap (Sapper) or Harpoon (Marine)
K First Aid Kit (Driver, Sniper or Spy)
L Lethal Injection (Spy)
M Submachine Gun (Driver)
Q Release acoustic decoy (Green Beret)
R Precision Rifle (Sniper)
S Stand up (Everyone)
T Release inflatable boat (Diver)
U Reuse uniform (Spy after he is seen killing someone)
W Pliers (Sapper)
X Knife (Green Beret and Diver)
1 Select the Green Beret
2 Select the Sniper
3 Select the Diver
4 Select the Sapper
5 Select the Driver
6 Select the Spy
7 Select the special guest
F1 Help
F2-F7 Split screen (1-6 screens)
+or- Zoom-in or Zoom-out
* Normal Zoom level
TAB Change the position of the knapsack on the screen
ESC Go to the Main Menu
CTRL+B See the mission Briefing
CTRL+S Quick save the current game
CTRL+L Load the last quick saved game
ALT+click Make the camera track the designated target
CTRL+click Shoot from an armed vehicle
SHIFT+click See the field of view of the selected enemy soldier

Use the terrain and natural features of the map to your advantage. Use rocks to your advantage and hide behind them. They're also great places to set ambushes for patrols.

Corners are the best place to set up ambushes. Stand around a corner and draw some attentions to yourself. Fire a shot or something. When the enemy comes around the corner, you can pick them off easily. Note this may also set off the alarm.

Crawl! Whenever you move anywhere you risk being seen. Crawling reduces those chances of you being seen and helps you to live on to fight another day.

Group your men together and use all of them to shoot. It normally takes 3 shots to kill a person but now you can do it much faster.

Garrisons will cause you a lot of back ache in commandos. The easy solution to these Nazi spitting buildings is to blow it up! Take a barrel or charge and demolish these things. You don't have to worry about reinforcements coming out any more.

Explosives are always good fun. Set a barrel or charge somewhere and attract some Nazis with a gunshot or two. When the Nazis come over, make them pay for their crimes.

When you try to kill a patrol hide behind an obstacle where you can pick off only one man at a time.

If you are getting shot at, duck or run, whichever is the best way. Duck if you are in the dark green field of view of the shooter and run if you aren't.

Kill everyone you come by. Even if they don't pose a threat right away, they might later on. But remember always hide your victims!