The first step in traffic building is to make sure there is some good fresh content on your site - ie. don't start a new traffic building campaign if you haven't updated your blog/website for months and if you have no quality content to put in the path of your new traffic.
Commenting is still a good 'organic' way of getting some traffic to your site, it can have the added effect of bringing you some back-links where the blog is 'do-follow' enabled (less and less likely these days). My preferred method is to only comment where entering a website URL as part of your identification is allowed. I use an anchor text keyword as my 'name' ie. if I were promoting this blog (which I clearly don't...!) I would use 'Website Building' or 'Web hints and tips' or whatever... Then enter my URL and in most cases this provides a free anchor text link if nothing else. The more 'niche' your keyword, the better the outcome.
In all cases I would leave an articulate, well-written and relevant comment which will probably guarantee a visit from whoever is validating comments, and possibly others who are following the comments on a long thread.
This is a long-form, but totally organic way of getting some authority to your site - these are the things I would steer clear of:
- Paying someone to leave comments on my behalf - the quality of comments would be dubious at best especially where the contract may end up in the hands of someone who struggles with the English Language...
- Leaving the same comment on every site - your comments should be relevant to the content, spam comments are only going to get deleted and then you are wasting your time.
- Leaving a link in your comment - even if links are allowed, I would consider it rude to blatantly place a link in a comment and would expect to have my comment deleted unless it was totally relevant and went to a third party site. Definitely NO affiliate links, that certainly would not endear you to anyone.