So, OP, assuming you're not incredibly vain, I presume you stand out physically rather than being in the public eye. If the latter, well that's the price of fame eh? If you're 7ft tall, then a Chewbacca outfit is my only offering.
All the advice above is sound. Be prepared, be natural, be confident, minimise your exposure in the open (e.g. get a cab to drop you off close to where you need to go). If you are really worried about it, do an outcall. Might cost a few more quid, but what price for less stress? It will ease you back into the game, and you could consider incalls in the future. Best of luck.