Be aware of the signs on the actual road too. Quite often they will paint the road name... So look at the map as you approach the roundabout, and follow the lanes with the same road name.
If in doubt, then do try the clock method, but do it with the map diagram as you approach the roundabout, not just the visual approach as it seems to you. If the exit is 12 o'clock or less, then left lane. If it's more than 12 o'clock, then the right lane.