It really does depend on lay-out .. your COAST skills , common sense
RoadCraft offers a little more help. Using COA - identify the hazards - scanning to the limit point, to the left and right. Use MIRORRS (all three

and consider an over the shoulder for that "idiot" on two wheels (who could just be
me 
as I do ride me bike and me motor bike as well as drive me cars!

).
You know which exit you want - so if turning left .keep in the inside lane and if turning taking an exit to the right then perhaps wise to choose the outer lane.. or L3/4 if one of those compicated efforts which require a lote of PSL/MSM/COAST and courteous negotiation on the part of all

I think this "courtesy" is important .. I twin it with Concentration in COAST - just as I twin A for ATTITUDE - part of our "acid lecture service"

and - we do not dish out fines all the tiem either. It should be a last resort or "no choice but .. given what we saw the person
do 
and whether we show our fangs or not - I think we should at least try to make the person understand why we take our stand and offer constructive advice... but I also think we should offer benefit of the training the public kindly paid for with courtesy and a genuine constuctive and positive criticism. It really defeats the objective of attempting to identify and get the driver to learn positively from a hard lesson if we do the "holier than thou - bossy prefect .. whatever routine which people out there can and will resent. I do think our team here behave professionally on the whole - and can only hope the negatives I do read on-line and in the press are exaggerated "bad day affairs"
But back to the topic .
Once you have decided exit... based on the COA sweep of the road and lay-out ahead . you plan your accordingly.
You lose the speed smoothly .. and your speed of approach will be planned and decided by your COA - view of the roundabout and traffic already on it.. you plan to sopt but should be also ready to go!
Your gear choice depends on your COA of the traffic conditions
Consider whether or not to signal - and this does depend very much on the courteous requirement to let other road users know what you intend to do so that they can plan accordingly.
Your COA should alert you to traffic already on the roundabout and approaching cars from other exits
You should be prepared to stop .. but ready and looking for opportunity to go .
When on the roundabout .. you blend into the traffic already there without disrupting it. In other words .. you look to match the speeds on the system. Keep COAST-ing whilst on the roundabout.
You know your exit .. so you use your nearside mirror and centra with a split second darting glance on the offiside one l to check it's safe to move into L1 if you have to - dependent on the markings and rather confusing paints on the tarmac at times . Then you enter the road you want and accelerate smoothly away.
But yes

some roundabouts need extreme care and the Highway Code advice is helpful as a "rule of thumb" - and where - for the benefit of my lovely cousin Wildy who posted about it being viewd as "jsut a code at times" a court may sometimes take the view of "code" unless designated as a MUST per the ROAD TRAFFIC ACT 1988
But Rule 162 is still a good place to start. It's where the this advice meets complex roundabout from hell that we can run into problems. Common sense, human intelligence and decent human courtesy and maybe subconscious COAST applications usually see us through these complex roundabouts safely 95% of the time
I congratulate Johnny for his comment and will agree that only a first class A star grade numpty could reply to him per his OP here .
Roundabouts should not pose much problem .. but I am reminded of Papuamau who per Marianna who posts at intervals to his site says he is a really lovely and sensible chap (and he did agree with me of course

at the time

)
As I recall he wanted no roundabouts at all but cross roads with a BiB orchestrating the traffic like the conductor at the Last Night of the Proms"
I think I admitted to causing absolute chaos as a raw green shoot of a young officer once.. (I caused aboslute gridlock.
in the middle of London
I do not honestly know what I did wrong to this day... but somehow drivers misinterpreted me .... and I had an embarrassingly awful problem to deal with .. and am still thankful and grateful to my colleagues and guv at the time for bailing me out of a msichief there
and if anyone reading was held up in the West End of London in the early 80s because of a numpty rooky directing traffic after a power cut .. I am truly sorry!