Content is King. You have probably heard about this before but if not, I will tell you that “content” is what matters on the web. It is also true that a good looking design helps a lot. However, the idea is to find a good ratio between a good looking design and a “rich unique content” Blog. When I design or tweak a theme, I look for a clean and nice design. Anything too heavy is bad for you, for your server and most importantly, for the search engines.
A heavy design, full of spectacular graphics that look amazing for the average eye, is going to load too slow and sometimes, crash or freeze a browser. The search engines want your content, your unique posts written by yourself. Also remember, it is very important to have a text logo instead of an image logo. I have seen very good looking themes from talented designers, but they totally forgot about this point. Having a text logo, instead of an image should be mandatory for all themes, because they tell the search bots, what the main heading title of your Blog is. These are my two cents for now. 🙂