You would use FB to generate interest and to get people to like your page. FB would be a slow burn as you gathered followers and keep posting relevant/helpful info. Trying to use it as an advertising method to generate leads would be hard to be honest.
Advertising, as in a 'Need a bookkeeper - get in touch' type advert is not going to work well anymore, advertising has to be a long term strategy that builds trust.
There are plenty of marketing people on FB who provide free or cheap courses on how to harness marketing on FB, Insta etc, have a look at those.