When a visitor comes to your site, you have only a few seconds to convince him to stay. You want to put all the most important data above the fold.
Imagine walking past a newspaper stand. The headlines and pictures catch your eye. The newspaper is folded in half and all that eye-catching information is placed above the fold. This space is reserved for top stories, and pictures. Thus enticing people to buy.
In internet marketing this is also called above the scroll. The idea is to keep all that eye-catching and important data at the top of the screen. This would be your great headlines, your opt in box and your top advertising.
In the last year newspapers have dropped their old format and have gone to a blog look, still keeping it above the fold. The change is partly because of the amount of information that can be put in that blog look. Also newspapers are competing with the Internet.
There are many WordPress themes that will keep your eye-catching important data above the fold. How much information you consider important will determine if you want a one or two column sidebar.
No matter what you choose. Keep your lay out clean, easy to read and navigate.
Go take a look at WordPress Blogs you like. Were you enticed to stay the second you clicked on the site? What features in the sidebar do you like? Did they do a good job of keeping the important data above the fold?