Kick-ups are a club juggler's insurance policy, if you are on stage and you drop but recover with a decent kick-up the audience may well be more impressed than if you had done the original trick flawlessly. Kick-ups also save you all that bending over and grovelling around on the floor, which is so often needed when working with balls and rings. Probably the best way to learn kick-ups is to read the theory, and then every time you drop a club when practising have a couple of goes at kicking it back up.
A short note about clothing: most shoes or trainers are OK although some big boots may present problems, something that jugglers often overlook is the type of material which their trousers/tights are made from. This might sound odd, but I remember once preparing to juggle at a fashion show - I had checked that I could do kick-ups in the shoes, but it wasn't until the first club shot off into the audience that I realised the smooth material from which my trousers were made was too slippery by far.