Starting with laying on my front I do tend to close my eyes, largely as otherwise I'd be mostly looking at the floor (on a proper massage table with the face hole) or left/right with normally not a huge amount to see. My arms normally by my sides, if I bring them up and rest my head on them they tend to go numb after a while. I don't tend to do much in terms of touching when I'm on my front, maybe if she is pushing against my hand I'll have a littel stroke of her leg -but for me I don't find it that easy to move my arms when laying on my front. The only exception to this was one girl I found, would stand by my head and reach over me - and if my hands were at my hand I could reach around and fondle her arse.
If I notice she's getting close to my manhood, then I'll open my legs a little to help, and possibly raise my bum. But I've never moved onto all fours or anything like that - but guess they'll be a first time for everything.
On my back I keep my eyes open, hand by my sides. Then often I will just ask if it's ok to touch, and 99% of the time I've been told it's fine. So I'll start off with stroking her leg, and going exploring. I always say, if there is anywhere you don't like me touching just say and I'll stop. Apart from one girl who didn't like me fingering her, could play with her clit but not inside, no-one has every stopped me touching what I like.