First, don't worry about offending anyone.
You get what you ask for so being shy is not good.
Just don't be rude whan asking. Be polite. Like asking where the milk is at the grocery store.
Once sure sign to the girl that you are looking for HJ, BJ or FS is to take everything off, don't leave on your tighty whities or boxers. Cover your ass with a towel. When she comes in if she lifts the towel to see what you have on thats a good sign shes WG. And being nakid sends the signal you are there for more. If possible flash her your rock hard cock.