Blog audiences (and for that matter audiences for most content) are primarily built word of mouth (or perhaps today I should say tweet of thumb). Yes, you have to seed the process by making the existence of your blog known to as many people as you can, but after that, it is all about the retweets and the facebook likes etc. etc. that other people do.
I track the stats on my blog pretty regularly and I can tell you that just one tweet from someone prominent in the field can send the views through the roof. Usually they settle down again, but thanks to the blitz that one tweet provides my regular audience grows just a little, and that increases the chances of the next big blitz happening.
And, of course, the more linkbacks and tweets and likes you get, the more Google takes notice and you climb us the search rankings for your topic and that bring in more pure search visitors, and some of them become part of the regular audience and so a virtuous circle is established and your audience grows, at least to the point where you saturate your available market.
But what provokes all those tweets and likes and shares? Great content. The Web is full of content. Very little of it is any good. You can promote the heck out of bad content and you will get nowhere at all. If you just seed your local area with references to great content, however, word of it will spread and your audience will grow. The best thing you can do to grow your audience is to create great content that people love to read. And if you are promoting the heck out of your content and your audience is not growing, that is probably a sign that you have not figured out how to write the kind of content people want to read yet.
There are a ton of film blogs, and a ton of people interested in film. But the audience never gets distributed evenly. Just a few sites will attract almost all of the audience. That is just the nature of the beast, and part of the effect of word of mouth: success breeds success. So, if you want to grow your share of that audience in that crowded market, the best thing you can do is to figure out what you can provide to that audience that other film blogs do not. Can you be different? Can you bring a different perspective? Can you be wittier or more perceptive than other critics? That is where your real audience growth is going to come from.