A good way to propose would be to take his girlfriend for dinner. At the same time, let him order a cake and have the proposal ring inserted on the crust. Let her cut the cake from the side the ring is and she will bite it and realize a hard thing in it, which she will find out it is the proposal ring. Check out more tips from http://www.wikihow.com/Propose-to-a-Woman.
If he's into tattoos he should get one that says, '[her name] will you marry me?' then when he's with her, wrap it up and ask her to look at it to see if it's infected and then she'll see it and be amazed lol