Purpose: To keep traffic moving - allowing traffic from differend directions to merge/cross without necessarily having to stop.

Priority: Generally traffic already on the roundabout and traffic joining from the right have priority. The direction of travel is always clockwise - Give way to the right (if it's clear keep moving). Sometimes traffic on the roundabout has to give way to traffic joining (look for road markings or signs). Traffic lights also determine priority.

Advance Information: Look well ahead for signs. Large/complex roundabouts also have direction signs showing the layout (these help you to plan ahead).
Look out for land markings and choose the correct lane early. Dont straddle lanes or change at the last moment.

Hazzard: All junctions are hazzards - use the MSPSL routine on the approach.

Speed: Slow down on the approach (2nd gear) , and allow time to asses traffic already on the roundabout.

Look: Look across the roundabout to identify your exit and any potential hazzards.

Hazzards: Keep an eye on the car infront - it may stop while you're looking right (common)
Pedestrians - crossing on entrances/exits (they may cross even if there's no crossing)
Cyclists/Horseriders - tend to keep to the outside (left) even when turning right
Motorcyclists - Difficult to see
Large vehicles - May take a different course (watch for signals and the rear cutting in)
All vehicles - Be prepared for them to cross your path to leave at the next exit
Surface - Can become polished and slippery - avoid harsh acceleration or braking

Mini Roundabouts: Approach as a normal roundabout but Slower - there will be less space to manoeuvre
May be insufficient time to signal left to leave the roundabout
Pass around the central markings (nless you are a large vehicle or have a trailer)