Girl wants to go down on me, what to do?

So my ex-girlfriend is so horny all the time, and she is coming over in like a week. She just told me she'd do ANYTHING I wanted her to do. So...I'm wondering how I react if she ends up giving me a bj (going down on me). And where is an appropriate place to get one when there is other people at my house? Thanks in advance. I plan to shower and shave beforehand so...no worries there.