KISS - Keep it simple stupid. Always keep your blog simple, organizes upto the point. Do not over-flood with unnecessary posts or irrelevant images and keep your content straight-forward.
Write from your heart! Be original and make an impression!
Formatting - Your post need not be a circus. If you are not good with formatting, then stick to a theme that is light and descent in colors and the post layout. If you are good with trying new stuff then use that skill to better express through colors, fonts and layouts. Avoid colors that are dark and fonts that are overtly bright.