There are several free ways you can improve your traffic and you have already mentioned some:
- the optimization of the content on your website
- sharing the new posts on different social media channels (Facebook, Twitter, LinkedIn)
- comment on others' website with the aim of posting such an interesting comment that they would come and visit you on your www
- engaging in conversation on LinkedIn on groups that are relevant for your website in order to have a direct contact with your group target and maybe respond to some of their questions in your future articles
I am currently working for a start up and we are testing each of these channels in order to draw some conclusions about what drives traffic to our website. So, if you have any interesting marketing experience to share about your traffic, that would be very helpful for me.