a pro uses a special tool that shows the bent in two directions horizontal and vertical, but later more of that. With a little practice you can do that on your own.
First of all you will need a good spoke key, my favorite brand is Spokey. For normal bikes you will need the red one and for mountain bikes the black one. The link from 040304 shows the technique quite well, but I'm doing it a little bit different.
The bent has a given length, at the beginning a little bent, that gets more until the middle and then less to the end of the bent.
Depending on how much the rim is bent i would start at the beginning of the bent with something like an 1/8th turn of the nipple then increasing until a full turn at the middle of the bent and then decreasing again to an 1/8th turn at he end of the bent.
Then turn the rim and see if it hits the brake pad and if yes, how hard and is the length of the bent shortened. Repeat that process with a decreasing turn angle until the bent is gone. At the end you will need a very little turn angle like 10°.
If the bent was to much for the rim you will notice that the bent from brake pad to brake pad is gone but now you have a vertical bent. That's the reason why a pro uses a tool that shows the bent in both direction at the same time.
For a normal bent the brake pad method will do the trick.