You can either use the "A" handshapes, like I do below, or you can grab onto the upper arms with "curved hands."
A single movement tends to be the verb form of "give a hug."
A double movement tends to be the noun form "a hug" or it can mean the process of "hugging." You might see some people twist the torso a bit for emphasis, but I wouldn't unless I wanted to describe an extended (long) hug.
HUG: Note: Deaf people hug more than Hearing people do. It's a cultural thing.
American Sign Language University ™ ASL resources by Lifeprint.com © Dr. William Vicars