Choose a template that suits your blog content. It not only adds to the blog's beauty but will also accentuate the content well. Bad design is always a put-off to readers.
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.
Its not just good content that matters, presentation of post is very important too. Have attractive pictures, fonts etc to hook the readers.