Junction-pair

Roundabouts are good for keeping traffic flowing.  They were invented in 1909 and standardised in 1966.  They can look very complex, but think of them as either:
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​(1)  a crossroads with a circle in the middle, around which you drive clockwise (mini-roundabouts); or
(2)  a one-way road curving tightly to the left, into which you emerge before turning off (medium roundabouts); or
(3)  a pair of junctions: a T-junction followed by a left turn off a major road into a minor one (big roundabouts)

(2)  helps you remember priorities.  It's the same as when you come to a T-junction from a 2-way road into a 1-way one: you give way to the right.

​If busy, that 1-way road may have multiple lanes.  Keep in the one you emerged into.  Then watch out for directions marked on the road, or on signs, in case you need to change lane BEFORE you get to your exit (your left-turn, into a 2-way road again).  It's about making well-timed choices.

(3)  helps you see the roundabout as a pair of junctions.  So, use the hazard routine ("MSPSL") on approach to the T-junction part.  Then use it again to leave the roundabout (the "L" turn off).

Time starting your MSPSL so you signal left as soon as you've passed any left-turn before yours.  ​That way, no one gets confused about your intentions: they can plan when and where to safely go.  Remember: "signals are to help and warn, but not confuse".