If you are thinking of starting some good advice has been given already, and yes it is physically draining especially when you get 2-3-4 hour sessions, let it flow if you know what you are doing, if not you will find you are just stumbling through the session, a lot of PD's have tried and just think give them a quick whip or stick a strapon on, it's not about that, fantasy and fetish with a great imangination is always key!
My advice don't look at the American Porn Pro DOMME clips, look at British ones or German, get yourself a website done, get on as many fetish sites as possible, and as nia suggested get a lot of equipment, I have spent umpteen thousands and have bespoke furniture, and clearly set your limits, I.e do you do SCAT? Needle play....etc
You get a lot of TW's but there are serious submissives who want the correct session, and will tell you what they want down to the tee, but foremost you are in charge, they listen and act, you are there superior when in your presence, don't ask ' is this ok for you?' Set rules at beginning and if you are doing full on BDSM session set clear the rules and if needed code words at beginning of session, and don't just jump into a full on session straight away, also learn how to spank and whip without leaving marks! That's a good one as some love it but remember they have families and partners, it's an art!
Hope this helps