Increase website traffic

Content. Content. Content.

If you are an established operator, you must have a pretty good understanding of who your client is. Create original content that peaks the interest of your core client base.

If you are a startup, first decide what clients you want to attract and then create content that would be attractive to them.

Mix that with some trusted SEO strategies aiming at the market you are trying to reach.
Aside from content on your own website, think about content on YouTube - especially how-to articles in the web hosting world. It's different for different industries, but I've seen a lot of success with posting how-to, semi-technical, and extremely basic videos on YouTube. Oh, and then you must promote them at various outlets - get social.
Social sites can be very helpful in increasing traffic of any website. Especially, if you know how to use reddit, you can certainly get lots of traffic from this amazing website.
On site SEO and off site SEO - I would probably place those two in top positions for organic traffic.
Yes, content is key when it comes to organic traffic, but it also needs to be a bit optimized around keywords you are trying to compete for.
Social media and forums that target your niche is something to also consider.
Good luck! :)
SEO, YouTube & social media such as Facebook, Twitter, etc. are the usual low-cost organic ways, but they can take time to build up.