There's no better place to read between the grip than the hug. It's like a gauge of human emotions. Weak, halfhearted hugs are disappointing and can demonstrate obligation or distraction, but it's the hug that goes from friendly to let's get a room that I'm interested in. Learn how to discern the we're-just-friends hug from the something-more — and more — hug.
These hugs may be longer than a hello hug between girlfriends, but the we're-just-friends variety works like this: Your arms go below his shoulders while his go around yours. His hands may wander if you stay long enough, but really shouldn't go beyond your midback or upper arms. There may be a quick peck on the cheek, which you can analyze based on previous hugs or if he kisses other girls. A longer hug when one of you is comforting the other rarely means anything beyond friendship, but can!
If the friendly hug gets friendlier then something more may be behind it. When chests touch while both people hug each other's shoulders, it's considered a heart-to-heart hug. It's definitely a sign that there's more where that came from. The placement of hands is also key. If hands wander longer and farther than normal then it's probably not your imagination — but his!
Whether you're in a relationship or not, if there is lower-body contact then you two are either having sex or will be very soon. When a guy hugs you from behind (hopefully you know him . . . well!) then he can't wait to be alone with you. Longer and tighter hugs signal intense feelings, and they demonstrate commitment when done in public.