This post follows on from – How To Choose A WordPress Theme -Free, Premium or Custom
When choosing a theme you must consider design, layout and functionality.
When considering these, keep in mind the general type of theme you are looking for (see previous post). If you are looking for a free theme, you need to find something as close to what you want as possible (or be savvy enough to tweak it yourself). If you are looking at Premium themes, you may have some flexibility on colors and admin options. The closer your theme is to what you want to begin with, the less tinkering you will have to do. Determining what options the theme gives you will be important.
Remember as you are looking at themes that colors and fonts are easier to change (with a little CSS) than things like sidebar placement, and changing the layout/ structure, unless you’re comfortable with PHP.