Large roundabouts (Especially in bigger cities like London)

So I've been driving now for around half a year quite regularly though and I feel pretty confident with most things. The one thing I am still struggling with though however is Large Roundabouts. My town is quite small so there aren't many of these here so I'm able to avoid them usually and when I go past them on the motorway they tend to be not too full so it's usually not too bad if I end up in the wrong lane or make a little mistake. However, I have some family in London so I want to be able to drive up there more frequently. The only problem is it seems to be full of these larger multi lane roundabouts and I have no idea how to navigate. Ik ofcourse they tell you to just follow your lane towards your exit, however, I always struggle to figure out which lane I should be in. My satnav will usually only tell me the name of the exit I need to take but the road markings tend to tell me the name. Of the road and usually they're quite worn out aswell. So I usually end up getting in the wrong lane and either having to quickly switch or take the wrong exit. Does anyone have any advice for me to know quickly which lane to be in when using a large multi lane roundabout, perhaps without relying on too many road markinga if they're worn out. Thanks