Preparing before spray tan is crucial. What you do can mean a difference between a good and a bad spray tan.
The spray tanning solution affects only the dead skin cells. Your skin has a build up of dead skin cells on top of it. The thicker the layer, the sooner it will rub off. If you exfoliate, the layer will be very shallow, and it will take a while for it to “build up”. Your tan will last longer. It is important to use either exfoliating glove or products that don't contain any oils, otherwise the oily barrier can stop the spray tanning solution getting through.
Many deodorants will stop spray tanning solution going through. Some others will turn the armpits green (you can imagine my horror when a client came out of change room with green circles under her arms- I never forgot to make sure nobody else made that mistake).
Few moisturizers and makeup products can act as a barrier, not letting the full amount of the solution to attach itself to the skin (that said I had very many wonderful tans with moisturizers and make up on- but you never know which ones will mess the tan up). As soon as you've had your spray tan you can apply deodorant and make up.
Although you wipe off the excess of the spray tanning solution with a towel after your session (booth spray tan), or dry out in front of a fan (airbrush tan), the tan needs to “set”, and the process will take about an hour. It is best to bring clothes and shoes as loose as possible to wear after your spray tanning session, to make sure nothing rubs off.
If you need to shave or wax your legs do it definitely before and make sure that you wash your legs after waxing to remove any wax residue. If you shave your legs after spray on tan, you will take off some of your tan with the hair.
If you will be sprayed with the solution containing bronzer it is best to shave or wax one or two days before, as the bronzer gets into the newly created pores and can give you "spotty" look. If the solution is clear that is unlikely to happen.
Those steps are quite necessary before your spray tan, unless you want to spend some time and money experimenting...