Main tip from me is "don't use the boost post button". I wrote a, now really outdated, blog on it a while ago.
Other tip is don't fall into the "as many people as possible" trap. You don't want as many people as possible, you want as many people who already love your pub but don't know it exists yet. That comes from analysing the current patrons of the pub, finding the actual patterns (no gut feeling here), and then replicating that audience through Ads Manager.
If you can be strict with yourself on both of those counts, Facebook Ads are some of the highest ROI spend you'll make online.