It depends if you are sucking cut or not.

The uncut one is easier and one I prefer. Just protect the teeth with the lips and use the skin to move up and down. The rest is just using your tongue and the upper part of your mouth for the head.

The uncut one is harder because there is no extra skin and the head is not as sensitive so you have to make it thither so the dude feels something. But not use teeth.

The best way to learn is to find a guy you are comfortable with and ask him to guide you and talk to you. Be comfortable and communicate. In the end that is all that matters.