Never mess your blog with too much of Adsense ads. It gives a confusing look to the blog.
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.
Always let the picture do the talking! As a picture speaks a 1000 words.