The map/diagram helps people not familar, the only really complicated thing is making sure you get in the right lane, and keeping an eye on those around you.
Then I started paying attention to the displayed layout. This helped me with the bearings and lane positioning. At least, that's one item off my list when I'm in the roundabout.
Ideally the sign would be 1) Rotated so that the driver proceeds from the base towards the top or sides. 2) Clearly depict the LOGICAL layout (bent slightly towards the physical) of what flow patterns _do_ during the roundabout from that input. 3) Also clearly depict which exits go where.
There should really be two signs actually, one before the diagram that lists (locally relevant roads / landmarks) by lane for sorting (if there's more than one lane in).
PS: The route map should also add a YIELD sign in mini next to the entrance with an according broken line. The interior lanes of roundabouts always have priority and all inputs are yield merges in.
Then there is the less obvious stuff that happens multiple times per hour, like entering in the wrong lane given the desired exit (even though it is marked), vehicles inside the roundabout yielding to vehicles entering the roundabout (even though there is signage), or vehicles entering the roundabout failing to yield to vehicles inside of it (same signage).
As for non-standard roundabouts, those can confuse just about anyone since people often don't realize that it is a roundabout.