As we all know, a big chunk of the world's population are on FB. And there are also countless businesses on it. So, what you do is find lots of businesses in the niche that you're aiming to target. Like those pages as your page, and interact with them a bit. As well as commenting on and liking their posts, it's also worth sharing some of them to your followers. The page owners – many of whom are also the business owners – will definitely notice this and get to know you a bit. That's worthwhile in itself.
After a while you'll have a list of pages like this in a specific niche. Then write a blog post that is specifically related to it and useful. Say you have an employment agency for the hospitality industry. You could do a blog post about what makes a really good barista.
So, the post is useful, targeted, and interesting. It shows your expertise in your field. But it's not overtly promotional. Then you can post it on their page. You're not spamming. You're helping them. Given that the page owners already know you, you'll get a decent proportion of them clicking on your post. Some of them will look through the rest of your website too.
Occasionally they will share it to their own networks, which can result in a torrent of hits. But even if they don't you'll still get some views from the pages followers.
This is a bonus but the main benefit is to be seen by the page owner. Some of them may become clients. But even if they don't they still know you and respect your authority in your field. That's valuable for obvious reasons.