We find it helpful to complete both processes in the kitchen sink, under cool, running water. Have a colander handy to toss your peeled shrimp into, and a container handy to toss your shells into - if you plan on saving them for later use..
kitchen shear method
Cut down the entire back length of your thawed prawn. The shears will penetrate the meat slightly, but it'll be unnoticable once cooked.
Peel open the shell, to expose the meat.
Remove the meat from the shell, and note that you may have to give the tail a small squeeze to slide it out.
Standard peeling method
Starting at the "head end", hook your thumb under the first section of shell
Peel back the first section, exposing about half of the meat
Repeat with the next section of shell
We'll remove the last portion of the shell by pinching the tail, so the meat slides out