There are various sites you can advertise on (freelance writers sites, easily Googleable) - when I started out it was free but I think they now charge an annual fee. You should also have your own website, of course, and get some advice on how to make it come up top on Google. And be specific about what kind of ghost-writing you'd be willing to consider...lots of people want their biography done, I found, but don't want to pay you up front for it. Avoid them like the plague!
Fees for ghostwriting can be a bit hazy, so work out some basic prices by doing a bit of web research (I'm too out of touch now to be of use, unfortunately).
There's lots of proofreading work to be had (freelance editing sites also Googleable) but I found it didn't pay quite as well and it also ended up boring me to tears, but then I'd had years as an editor in-house and wanted to move into writing so anything that wasn't writing tended to get right up my nose.
If I think of anything else I'll drop you a WWmail.
Emily