Thankfully, you don't need to spend a dime to figure out where a large portion of your audience can be found on the web. In fact, you probably already know a few blogs, forums, websites and social media communities where discussions and content are being posted on your topic (and if you don't a Google search will take you much of the way). From that list, you can do some easy expansion using a web-based tool like Google's Display Planner:
If you're someone who can produce graphics, take photos, illustrate or even just create funny doodles in MS Paint, you should leverage that talent on your blog. By uploading and hosting images (or using a third-party service like Flickr or Niice to embed your images with licensing requirements on that site), you create another traffic source for yourself via Image Search, and often massively improve the engagement and enjoyment of your visitors.
Choose content that will last for a while. This can be difficult depending on the style of your blog, but if you focus on writing articles that aren’t ‘trendy’, you’ll likely have many more readers in the long run. If you’re writing about a fad, insert it into an article that will likely stay popular for more than a few months. In this way, you can almost guarantee future readership, especially if your page gets plenty of hits to start. Writing about things that are popular in the moment may give you a short burst of readers, but after a few weeks the number will likely dwindle significantly.

Make sure your content is worth sharing and that you're actually phrasing it in terms that are useful for their followers/fans. (otherwise you're goign to come off ungeniune and spammy) In all fairness to, you'd want to develop relationships with the most influential rainmakers, ask them up front if there is anything you can do to help them out. Most of the time just asking is enough to impress them and develop a good rapport.
As you can see, there's all sorts of great insights to be gleaned by looking at where visits originate, analyzing how they were earned and trying to repeat the successes, focus on the high quality and high traffic sources and put less effort into marketing paths that may not be effective. In this example, it's pretty clear that Facebook and Twitter are both excellent channels. StumbleUpon sends a lot of traffic, but they don't stay very long (averaging only 36 seconds vs. the general average of 4 minutes!).
