Wolfenstein

This one is very easy!
When u get the shield just dont shoot the enemie who will come after u got it. Just wait for the achievement :) takes about 1-2 minutes....

After you've completed the campaign, go to the notebook and choose to replay the caverns level where you gain the veil power for the first time: on your way out you'll come across an MG-42 nest at the top of a set of stairs: Activate the shield and let the MG-42 bullets hit it over and over. There's a barrel of the blue stuff nearby, so when your meter runs out just press Y on the barrel to recharge the veil power meter. Then reactivate the shield and block the MG-42 shots. Keep doing this until the achievement unlocks; it won't take very long.

Try and stay away from the barrel when you're blocking shots, since stray bullets can hit it and blow it up. If you want, you can pick up the barrel and move it into a small alcove to protect it from gunfire.

Very Easy!!! Just like above when you get the shield no matter what difficulty just keep the shield up and sit in that room next to the crystals and your shield wont drain your veil amount at all!! and you can have fun with this you can sit in slow mo too!

If you missed this on the crystal level mentioned in the other solutions, and don't want to replay the level, there are two methods just as easy, it just takes a few minutes longer. On any level where there are two or more enemies around a corner from an energy pool, charge your shield, head around the corner, turn it on and get shot at, and right before it runs out, head back around the corner, charge it again, and repeat. Another option is to stand in an energy pool where the enemy can shoot at you, turn on the shield, and turn it off when the enemy is reloading. It charges pretty quick, and you can take a few hits, then turn it back on and repeat. If you don't have the reflect bullets power, it will be a little quicker, but if you do, just make sure to stay at least 30-40 feet away from the enemies, otherwise the bullets will bounce back and kill them. Should take less than ten minutes either way. The other option is to find an energy canister near enemies, put up your shield, and stand by it, taking energy whenever you need it. Unlike energy pools, you can get a canister refill even while using veil powers. Just beware that you run the risk of an enemy shooting and destroying the canister if you accidentally let your power run out. But this method is a little quicker than the one above.