I've had the same pareu for the past I don't know how many years already and I love it!
Most of the time I'll use it as a wrap around my waist especially when I'm at the beach and I'm feeling self conscious walking around in a two piece.
It also comes in handy after taking a shower while camping. The simplest full body wrap method I know of is holding and extending it as if you were to wrap yourself in a towel. You can adjust it to the appropriate length by folding it in a bit. Bring the sides to the front and twist the top two corners (not too tight!), eventually cris-crossing by the neck. End by tying the corners in a knot behind the neck.
There are a lot more ways to do this, but I really suck at giving directions. I apologize in advance if the above directions don't work!!!