The honest answer: mostly by keeping the ones you already met, then making yourself findable for the thousands nearby you haven't.
Acquiring a new client costs five to seven times what keeping one does, so if 65% of your first-timers never come back, more marketing just pours faster into the same leak. The highest-ROI “new client” is the one from last month who was one automated nudge away from becoming a regular.
Fix rebooking first: ask at the chair, automate the 4 to 6 week reminder, make loyalty visible. Then, and only then, is a new-client push worth the spend.
Simple division on government labor and population counts says there are on the order of 4,400 people for every working barber in the US. You don't have a demand problem, you have a discoverability problem. The clients exist; the question is whether the ones nearby, searching right now, can find you before they find someone else.
Being findable means a real page (your work, prices, reviews, one booking link), showing up in local discovery feeds, and, where platforms offer it, paid placement in your own neighborhood rather than ads sprayed across the city.
Your best marketing channel charges nothing and sits in your chair every twenty minutes. Work it deliberately: