On the first mission (training mission), when you first pick up the gun, do everything your instructor says until it comes to grenade training. When he tells you to pick up the grenades, you should already be crouching down. Turn and face towards the table you picked the gun up off of, and enter ADS mode. This is only to make you move slower. When you are right in front of the grenades, exit ADS mode and stand up, in that order. You should now be standing on the table where the grenades were. Move forward, and you will get off the table and be able to walk around and look at the scenery from close up. Its not really useful since the training mission is pretty darn easy, but it is fun. If it doesn't work, just try it again, it usually takes me a couple tries to do it anyway. You won't need to restart the system, just repeat from when after the person tells you to pick up the grenades.

When you have killed all of your enemies and your screen is flashing red wait for a little while. You will regain all of your health