It's not easy and it's not quick. When you make a website which involves user activity, it may take a year or two to see results you want to see. To get something back for your investment. In the mean time, don't give up. And play it fair, don't spam around and buy likes or something, because you'll be punished.
In my case, I put up vehicle classifieds site, which obviously isn't something new. But that isn't necessarily a bad thing. Always keep an eye on the competition.
So how did I get people to my site? Well, I went to competition sites and
kindly write to those who had ads there if they want to add them also to my site for free.
Think what users want. They want to sell their item and spend little money to achieve that. So, free is the best option. Also no one will pay you to be seen by 10 users daily.
But I didn't stop there. I went to car dealers websites who sell used cars and write them too, I presented my site and offered them free ads even for companies.
Also I write to car magazines, who will not post ads, but mostly have large database of fans on social networks, so I offered them banner on my website in exchange for sharing my site on their facebook page. I also add one more banner offer, valid in next let's say 36 months (when site will have more visits and ads), because if you have 10 ads and 50 visits now, they won't care if you put their banner on or not. You'll not be successful with everyone, but if one of them shares your site, that's already good and also free promotion
Improving your SEO is also vital, Osclass is still not quite good in that, but you can get websites to exchange links, so your site will have a better ranking in organic searches.
As for money, how will you earn anything if you have free ads? Well, it's simple. Free ads=more ads. So an user who would post for example Toyota where there are 100 same cars already, would like to have his ad more visible than others. There you have one way to earn money - Featured ads. Top of the category for x$ per week or something. Another one is Adsense banners and the last one is selling banner space to companies. When 5000 people search on your site for a car, you'll surely find many companies who sell car parts, oils and other stuff, who would love to place a banner there. Bingo.
Well, that's my strategy, I can't say you'll make it, but just don't give up. After all, nothing from above does not cost you money, only time, so you've got nothing to lose and it's worth to keep it going.