It's quite the all star list of advice here, so I'll be a greedy monster and hope I can look good just by standing near the smart people.

I would agree with denu and ksst that in the moment there is a "do or do not" quality to D/s, but at the same time that doesn't mean that to be a submissive or to submit that you must give up 100% control. You can give up 50% control and determine whether the person you're with can be trusted with that, then try giving up 70% control, etc. You may reach a point with your partner where you find you are both at a comfortable level, or you may want to keep pushing forward. You can leverage limits, safe words, and a lot of open communication to decide together what you want to give up control of, under what circumstances and for how long.

It's by no means an all or nothing thing, and in fact you're much better off testing the waters slowly with someone new. You'll most likely find that if you build up trust in a person with a small amount of power exchange that then letting go with another step becomes easier.