There are numerous ways. The best way is the way that gives you the most comfort and control. Here are some ideas to try.

Some can pop heads with their hands and do 1 shrimp in each hand, and get both hands to pop the heads at the same time. THIS is not my technique. They place their thumb behind the head plate and squeeze as they push the head off. I have little hands, and I am not one to bruise them up if I can help it.

I use a simple aerosol can lid....I am fussy tho. I used to love the "Spot Shot" can lids and then they changed them. The best aerosol lid is a lid that is thin and not formed into a dull thick rounded edge. Some folks use tuna and cat food cans.

Using the cans or lids allows you to ergonomically pop heads off hundreds of shrimp and not get carpal tunnel syndrome. Place the lid behind the hard head plate, push down on the lid [will sever head from shrimp] and scoop head into sink bowl. Again....push down and slide head to side, push down, and slide head to side.

Note to members:  It sucks to me my friend, you end up in my pictures for training purposes

Note:  The black lid in the picture has a thin single clean edge, that really is what your looking for in a lid selection. If you see a woman in Wal-Mart popping lids off the spray cans in the cleaning aisle, it is probably just me looking for a new Oak Hill fillet knife.