A D/s relationship IMO is really not that different to any other. When you had your first kiss, I bet you didn't think too much about it....

The best way to be prepared is probably to make sure you & your partner care for & trust each other, that you have good communication, & take it nice & slow.

As W/B said, it's not all physical- far from it. As lily & jeanne said, it's important to be secure in yourself- again, that works in any relationship.

Just do it- how you feel is what's important, not the technical details.

As far as the other person being knowledgeable, I disagree. For one thing some of the lousiest Doms are quite knowledgeable re the technical side of things, but have no concept of caring or communication. Also, it's a whole lot of fun with someone who doesn't know a darn thing- trust me!