Here's the long version.
If you can reach the bottom of you tank easily, don't use a net. Plecos are easy to catch. If you can't, either use a ladder and drain half of the tank. If you are too lazy to do that, and MUST use a net, it's ok to trap them in the net, but don't lift them out of the water in the net. You'll end up hurting them with the net most of the time.
The easiest way is to guide them into a corner of the tank, and try to have them swim into the center of your palm. Place your thumb on it's forehead between the eyes, and scoop the rest of your four fingers onto it's belly. Lift! If the pleco is giving you problems picking it up, lighting apply pressure on it's forehead against the bottom of the tank, that'll stop it from moving around, and scoop it up from the bottom of the tank with the other four fingers. For most of the plecos, the forehead area between the eyes actually are the smoothest area on it's back side. When you hold them this way correctly, that keeps the trashing around to the minimum, and the fins will be extended for inspection. It's mouth may suck on your palm or fingers, don't worry, they don't bite, at least haven't happen to me yet.
A very common mistake is the remaining four fingers, many just apply pressure on their stomach, the soft part, that actually stresses them out BIG TIME. you want to kinda support their weight mostly with your index finger and pinky finger on the pectoral fins. The middle and ring finger on the stomach area are mostly to guide and balance the fish. Notice my pinky finger supporting the base of it's pectoral fin in the following pictures.
When done correctly, they will be fine out of the water like that for extended periods of time. Most pleco can breath air, some can do so for hours easily, it's drying out that actually kills them when they are out of water.