I made a Facebook page for my work as soon as I started doing clients freelance, despite only doing one or two a week.
On there, initially I posted celebrity hair with tips how to achieve styles, photos of my own hair and the very few photos ofclients I did have - photos are like instant click bait, they drag the eye in so make the effort to take photos of every hair you do.
Before and afters always get me hundreds of likes, and often a lot of comments. I also did the odd 'Like and Share' competition at the beginning - ensure part of entry is 'Liking' your page.
If theres a festival, event or club night in your area, maybe thing about a competition just to do hair hair up or cut and blow on that evening for someone and a friend. You'll have to give up a couple hours of your time but you could get hundreds of new followers that will see all of your posts and eventually (hopefully!) book in.
I use photo editing apps like "Pic Lab" to create images of my work with fun slogans (one of my most liked ones was a photo of a balayage that had been mirrored saying "Hair is the only thing you wear when you're naked"). My clients loved it when I made these with their hair and always shared them onto their pages - straight away their friends would like their page.
It's also worth offering incentives for your clients - maybe offer £10 off their next appointment if they leave you a Facebook review, these help you look great and their friends will see they've written it. Or try offering discount if people post a Before/After!
When I started, if a new look came about, like the silver hair trend, I would post on my page with some of the most popular silver hair photos on Pinterest and write "I'm desperate to create this look, would anyone be willing to be my model for cost price?" and from there I would speak to some of the people who replied, and then work out who would be eligible for the look (and who's hair would be the most attractive, who has a lot of social influence in my local area, who posts a lot online etc) and choose them. Post some photos of the process to tease eager followers - no one ever believed the yellow bleach stage would at some point be a sterling silver haired fox! And your final image will be something everyone is looking forward to.
This is also a great marketing technique for showing off your styling - bar a few grips and your time, styling costs you nothing, so maybe post the odd photo of a fishtail plait or a fun hair up idea and say "I want to try this on Friday night, who wants it to go to ____club for a tenner?"
I'm now around 2.5 years into beginning my freelance journey and whilst I only have around 500 followers on Facebook, I am often fully booked for months at a time and at Christmas had to close my books. I have done social media for the salon I used to work in and also for the e-commerce business my boyfriend works for, so if you have any questions on how to utilize this for your business just ask - I honestly think it's the most powerful tool in your kit!