Go to Google and type in "escorts" and research as many websites as possible; keep the ideas you like and discard the rest.

Read the books and information that's out there.

Read the threads here on TER and especially pay attention to the providers you're most like on how they do it.

Read the self-help manual here on TER.

Make a website.

Get a hobby phone and hobby email; something that your SO isn't going to find or wonder about if he / she does find it.

Start posting ads.

Prepare for answers.

And always, always ALWAYS keep your screening skills up to date; screen out LE, creeps and other baddies as much as you possibly can.

Just curious. If you are in my area, I would love to help you get started.