I would say a very thorough knowledge of all types of the most common exotic pets would be a main requirement - so that you can ensure that they are looked ofter correctly in the shop, and also so that you can offer good advice and answer a whole range of questions from customers. This forum will give you an idea what is asked most commonly - the threads you see repeated endlessly here are what most new people to the hobby want to know.
Another very useful string to your bow would be experience in keeping the various exotics. It's good to have thoroughly read-up on all animals, but for example handling a 10 foot burm on a bad day is something reading books worth may not prepare you for.
Equally, a large amount of enthusiasm is crucial. Visit all your local exotic pet shops, get chatting to the owners and staff. Learn what you can about what they keep and sell, listen in on customer querys and soak up anything that may be useful. Make it known to the owners that you are interested in work and leave contact numbers for yourself in case they have an opening. Offering to do some volunteer work and help out with lugging stock about and cleaning cages will also show how keen you are.