When manning a machine gun, a short six or seven round burst works best against enemies. If a lot of enemies get close, lie prone and throw a grenade at them. Then, quickly get back on the machine gun.
Avoiding more attacks:
Sometimes enemies will just keep coming unless you move up. Keep moving forward to cover when you are not under fire.
Africa tank mission:
In the first tank mission in Africa, there is a Flak 88 gun that will take out one of your tanks. The gun is on the right side inside a building and is not visible. Shoot the second building on the right side. It is the tallest one and will start to crumble when hit. Also, some of your troops are on the right side. Do no run them over. They will help you by taking out the other Flak 88 gun. All you have to do is take out the two machine gunners on the right side after the first Flak 88 gun.
In the bomber mission, at the end it will allow you to choose any machine gun turret to defend the plane from. It is recommended, at least under the hard difficulty setting, that you stay at the back turret. It takes too long to get to the front, and your plane may get shot down.
Second to last mission:
In the second to last mission, after you finish clearing out houses of enemies, your tank will get ambushed by a Flak 88 gun and a mortar crew. You must first defend your position. Move into the shack building on the right side and move into the top right corner of the building. Watch out for enemies in the top of the building to your left. Once you have taken out all those enemies, focus on the enemies near the tank. Once you repel the assault, you and another soldier must take out the mortar crew. Follow the other soldier and keep your M1 Carbine out. When you get near the center of the town, duck behind the brick wall and pick off the two mortar men in the building in front of you. Then, charge up the steps towards the Flak 88 gun. If you sit behind the wall for too long, the Flak 88 gun will get you. Use your Thompson to take out the two men manning the Flak 88 gun, then plant the explosive charge. Run for cover towards the shack that you were defending earlier. Do not worry about the machine gun in the window; the Flak 88 will provide you with enough cover.
When you are going thought the dragon's teeth, take out the machine gunner and his friend in the middle tower. Then, make a run half way thought the dragon's teeth. Next, go prone behind a tooth. Take out the enemies around you and in the tower. Then, get up and run all the way through and underneath the last tower for cover. Wait for your squad to arrive, then storm up the hill and go into the bunker.