...and this is exactly what UKP is intended for. Well done Mr Dontbethatguy for taking the leap, and I think that's a really helpful set of replies you got there, so far. No cynicism, just helpfulness.
For my part, I'd also advise a friendly independent, over a parlour (even though Unit 8 has great reviews ... haven't been there myself).
Definitely be polite, honest and clear when you first contact her ... believe me the girl would never turn you away for being too vanilla. If anything it might even come as a relief for them.
I'd pick out somebody who people say is a nice person. Sounds a bit yuk but you're far better off with somebody who is thoughtful and considerate, rather than a WAG type who goes through the motions while checking herself out in the mirror.
Get it right first time and you'll probably find yourself becoming a bit of a regular with her too ;-)
Cheers and best of luck mate, G