Is it a commercial web-site?
If so, do you make money from ads (so traffic is key) or paywall, or whatever else?
Let me take explain something...
Assumption #1 you want traffic because you make money out of it
Assumption #2 you make money from advertisement, which is paid by impressions.
There are 3 big categories of traffic providers:
1. Search
2. Content Discovery
3. Traffic Brokers
Traffic Brokers
They are cheap (about 0.01$ per viewer), but the quality of viewers is questionable.
They rely on people mostly clicking stuff by mistake, popouts, and bots.
If the ads on your site pay by impressions, and they pay more than what you pay for the traffic then you can make some money.
The traffic you get is very low quality, with up to 90% of bots.
Almost none of those users will convert to loyal users.
If you reply on users paying for your content (buying, subscribe, etc.) then this is the worst traffic for you.
Even in the case of ads, this model is not sustainable in long term (you will never get the high quality & high paying ads.
Content Discovery
There are services like Outbrain and Taboola which brings traffic to your site, for a fee.
Prices are about 0.1$ per "click".
It's mostly human traffic, however the quality is also questionable.
Most of the users you receive arrive following "click baits" articles: ok for advertisement in your page, not too good if you rely on selling something.
You are good if about 10% of this traffic translates into more loyal users (people who will come back to your site directly).
Search
This is Google, Yahoo, Ask, etc.
Here the quality of traffic is very high.
Pretty much 100% human and somehow filtered.
You buy keywords and you will get people who searched those terms: so people that are interested in what you sell in your site.
The prices vary enormously depending on the keywords, but you get quality.
expect prices of 1$ per click... some cost MUCH more (see within spoiler)
Facebook
Facebook also generate traffic for you, for a fee.
It's somehow contextual, you can really define well the type of users you want.
e.g. "girls, 18-25, in New York, who likes dildos".
People will see your ads in facebook or promoted stories, and some will click and follow to your website.
Given that you can have fine-grain segmentations this is ideal if you have an actual service or content that you sell.
If you live by ads, this will be a too expensive channel.
If you have money to invest and a revenue model you can use a mix of the above to generate traffic.
Start with the cheap one to generate enough traffic to get into the radar of ads agencies.
After you are there you can work on improving the quality of the traffic you get.
Obviously you have to work on SEO (search engine optimization): techniques that help your ranking in Google Search.
Some general techniques are explained in various articles in the net, but to do a good job you need the help of an expert.
However beware... some techniques are "good" others are frowned upon by google and periodically stomp down on who use them.
And beware of charlatans, there are plenty of them.