If you get a 'spray tan' from an salon, be sure that it'll be dark enough for you.
Ask them if they'll re-do the tan for free if its not dark enough.
All I'd say is be prepared for when it starts to come off as the creases of your elbows and backs of your knees will be first and then you have to scrub the rest off. Owchhy.
Some people have said that St Tropez (from a Saloon) is okay, but again, I found that it was not that good. But then I was on holiday and it faded with me going in the pool, etc.