Depends on the roundabout...
If there're markings, you follow the markings.
If there aren't any markings, look at the road sign. If there is no road signage for the roundabout, go by physical location. 12 o'clock or before, left lane. Anything after, right lane. Road signage takes president if signage and physical location differ. If an exit is at 1 o'clock physically, but signage says it's a 12 o'clock exit, then it's a 12 o'clock exit. Beware of people wrongly using the right lane to take this exit.
Only exception would be if the 12 o'clock exit has two lanes, in which case the right lane can be used for 12 o'clock but you should exit into the right lane rather than the left.
Going through the middle on a roundabout that is obviously two lanes will almost certainly be a fail.