Find a Gap
Finding gaps on roundabouts can be tricky, here are some tips that will help you with roundabouts and passing your test:
Approaching slowly will give yourself more time to read the situation, assess the cars and find a gap.
Mirrors (Check for traffic behind that may affect your approach)
Signal (Signal your direction at the roundabout to help others know where your going)
Position (Select your lane on approach)
Speed (Change speed depending upon volume of traffic and your visability)
Look (Look for traffic approaching from the right and on the roundabout)
Start looking early; the earlier you start assessing the traffic, the easier it will be to decide when to go.
Watch for blockers that help you into the roundabout (see video of Balls Corner roundabout below on what to look for). Blockers are cars exiting the roundabout, blocking the traffic from the right but not affecting you, therefore creating a gap for you to enter the roundabout.