Roundabouts
Roundabouts are dangerous things, full of other drivers that don't know what lane they should be in, who they should give way to or when to indicate. Add diesel patches (overfilled diesel vehicles braking and turning suddenly for the first time since filling up), pot-holes (trucks lifting the road surface) and silly distracting landscaping, then they should be taken with extreme caution.
Gain confidence in what lane you should be in and when to indicate by reading up on the official road code.
The idea behind roundabouts is to improve traffic flow and therefore the idea is to keep your vehicle moving. Lane discipline aside, approach the roundabout, look at the vehicles on (or coming onto) the roundabout to your right and adjust your speed to try and get onto the roundabout with a nice safe gap. If you have to stop before entering the roundabout (no gap, poor visibility or traffic in front of you) then wait for a gap, move off, quickly check for a gap again (that's a 'lifesaver') then look where you're going. You see a lot of idiots going onto roundabouts looking to their right. There's no point in doing this as a) You've checked the gap twice b) You're now comitted so there's nothing you can do to avoid any other vehicle anyway c) The driver using their mobile phone who started moving off in front of you may have changed their mind and suddenly stopped. That's why there's so many rear end crashes approaching roundabouts. It may be 'their fault' but you're insurance company and the police won't agree.
The best advice at roundabouts (and indeed, motorcycling on any road in general) is to pretend that you are invisible every other vehicle/dog/pedestrian on the road.
Mini-roundabouts are a complete different beast. In New Zealand the safest option is to give way to a) any vehicle bigger than you b) any vehicle driven by an 'old person' as most have no idea what to do at roundabouts.
Lack confidence approaching or circulating roundabouts:- Go when it's quiet and go round and round the roundabout OR Get a friend with a car, "borrow" some traffic cones and make your own roundabout to practise on in an empty car park.
Confidence is best increased through experience. If you get too much confidence too early then it's usually followed by landing on your backside.