Add your personality - If you are writing on a particular topic, there are a number of people who will be writing on the same topic. So you need to add that specialty to your blog to make it look different and to allow your readers to take away something that the others are not offering.
Build a community - Connect with like minded people/readers to know what they expect out of you. Interact with them at regular intervals and take their feedback. It will help you gauge a trend and hint you towards a direction you want to take your blog to.
Spare time to read - Blogging is not just about writing but also about research and reading. Read as much as you can to learn new things and ideas that you can experiment with on your own blog.