Here's a good animation on the Wikipedia page for a 3 lane roundabout.

http://en.wikipedia.org/wiki/Roundabout

Khor, yes, I agree that you should stay way clear of trucks on roundabouts but otherwise you should stick to the lane advice given in the links. Trucks usually are not able to stick to one lane.

Qatar makes us all bad drivers because the majority of people do not obey or are not aware of the rules of the road. It makes you a good defensive driver though and aware of whatever crazy things may happen.