Always acknowledge a comment on your blog and respond to the commentator, preferably at his own blog. Its great to reciprocate the gesture.
Write regularly, neither too often nor too rarely. Two to three blogs a week is a good frequency to maintain.
Image speak - A lot of bloggers tend to ignore this, but the images on your blog speak a lot for what you write. Use good quality images and make sure they express your written stuff in utmost simplicity yet precision.