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.
Grammar - Depending on the language you use, blogging just makes it imperative that you are reasonably good with your grammar skills and proficiency if not a master. Remember your audience is a mix of both; the ones who are experts and the ones who are not.
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.