No shower before my tan?

Showering should not be done directly before your spray tan; after you have showered your skin is very dry and your pores are open (the spray tan can settle in little spots if your pores are open when getting the spray tan). The PH level of your skin has been stripped away from the soap and hot water, your pores need time to close and the natural oils of your body to return to ensure the best canvas for your spray tan. 

Shampoos, conditioners and soaps can have high pH levels which can neutralize the DHA bronzing reaction, and may result in less satisfactory tanning results. Give your skin time to balance its PH levels out before having a spray tan done.