there is no ' free ' way of getting traffic. even when you're using social media to bring traffic to a site, remember you're paying your electricity and internet bills to use a computer, and you use a computer to access your site, so whatever you do is not entirely free. in my opinion the ' free ' ways would take more of your time but there will always be a small cost involved. it's like a time/money ratio.
so change that mindset of ' free '. there's nothing free, as i said above there's always a cost involved with things one way or another. the cost may be money, the cost may be time. there's always a cost.
all in all i think the best way to get traffic to your website, and especially long term traffic is SEO. once you get your site ranked and slowly build links, you're building a long term asset. for SEO there are many guides but PBN's, Guest posts and high authority links should be included in your tier 1. ofcourse you can also go ahead and get expired and aged web2.0's, build contextual links to them as tier 2 and spam in tier 3. try using expired twitter accounts as well those work good too now adays. but what i'm telling you about SEO is like what works now adays, and it will save you a lot of confusion when you first start with SEO. if you have a competitive niche your cost will increase obviously but try to target long tail keywords in high volumes. 100 longtail keywords with 500 monthly traffic per keyword is 50,000 total ms. so do try SEO, it's one of the best sources of traffic you can think of.
^ tho this is not ' free ', it depends on your niche and competition.
honestly getting traffic to your site depends on what your site is about. first analyze what your site is about. then serach niches related to it on social media. see what your compeitotrs are doing, and copy them. don't plain copy them, try to do what they're doing in a much better way. So for instance if there is a FB page about your niche, that means you can create one too. if there isn't one then analyze whether you can make a FB page or not. after you've made it, start writing content and then share it to gather audience. now you can either spend a few $$ for page promotion, or you can create mass fake accounts and post in groups, or you can use FB like jackers. it all depends on you.
A similar process can happen with twitter. And with instagram. Let's not forget reddit. Thing is you can get traffic from anywhere, it depends on your niche and the way you attract audience. if you don't really know how you can get traffic from these areas then go to google, write
intitle:twitter site:blackhatworld.com
and all the threads which have twitter in their title will come up. read those, there are great methods on people getting traffic to their offer/site. if it's facebook you wanan use, type facebook instead of twitter in the above code. and then read those threads. remember to see what other people/competitors are doing. it's time consuming but worth it in the end TRUST me.
also try to use youtube to target long tail keywords in your niche and rank your videos in google, there was a post by
@ZlatanTheGod on how he made money with youtube by targetting long tail keywords but i hadn't had the time to see his full thread.
you can get traffic in lots of ways but there is no ' free ' way of doing it. if you want good traffic you need to have some sort of investment involved. be it small or big. you will require money in the future and trust me having some is always good.
hope that helps,
remember to copy your competitors. and do what they do, in a better and a unique way.