Not entirely sure what you're getting at with this thread, but if it's how do you make sure you get the best out of a punt with a submissive girl, I can give you the benefit of my limited experience.
Firstly unless you are comfortable and have some experience of being a Dom, be careful who you choose. Some of the experienced subs will expect you to do stuff you're probably not going to be comfortable with.
If you chose a WG who advertises BDSM and or Domination (receiving), it may be that's she's not a real sub at all. She might have a couple of whips or like a good spanking but may not let you do anything too extreme.
Having been with such a girl several times, it took until my third meeting before I spanked her ass, the reaction I got suggested she liked it and would be up for a bit more in the future. So I asked ahead of my next visit how much into BDSM she was. As above she told me she had a few toys and a couple of whips. During the meet i whipped her ass with a cat o nine tails and a riding crop. She encouraged me to hit her harder, liked seeing her red ass in the mirror. She also said she liked a bit of choking. Although I wasn't that comfortable with it I tried and she helped me out to do it right. I should have mentioned the important thing is to discuss and agree any limits at the beginning and safe words if necessary. I have to say choking a babe when she's gagging on your cock or fucking her brains out was surprisingly amazing for me.
I've had some more intense sessions with her since and have ramped it up each time. I'm meeting her next week when I shall use ropes for the first time. As far as changing positions and stuff, as this is my regular girl things tend to happen naturally and we are both comfortable suggesting different things to try with each other.
So I think the advice is;
Choose your 'sub' carefully
Agree any limits before you start and agree safe words which mean stop, no ifs or buts, you stop when she says it.
Be prepared to build up the intensity over a couple of meets, allowing trust to be established between you.
Only do something to her that you're comfortable with as you won't enjoy it otherwise, even though she might.
If you ask her if you can do something and she says no, don't throw your toys out of the pram. If she's comfortable with you she will ramp things up in future meets.
Hope this helps, I've really enjoyed my sub games but I'm not sure I could dive straight in on a first booking and expect to achieve what I've achieved over 4 or 5 meets.