As a new theme builder myself, I had to ask around on what I needed to know to build a WordPress theme.  So, I made a short list.  Here are the basic things you need to build yourself a WordPress theme.

CSS

Cascading Style Sheets are awesome.  They make your whole site look great (and uniform), and can even quickly make another site or project blend in.  (for example, ChurchCrunch and its forums)

You need to get familiar with this code because it will style everything on your site.  Setting up columns, the width of your page, what color your text is, the background, it’s all done here.

CSS is probably the easiest way to start with themes.  I used a stock theme and tweaked the .css file until I got something of what I wanted.  Once you get the hang of that, you’ll be ready for more.

HTML

Knowing HTML (or now, XHTML) is also a must.  You need to know what all of those tags do, how to code in an image, and what all that means.

After you learn some HTML, you can customize the look and layout even more.  Adding extra <div> tags to make new sections that you want to style separately makes the blog more unique.  And setting up a comments class to style your comment section.

PHP

Ok, php is where the rubber meets the road.  PHP is what WordPress lives in.  It’s a dynamic language that makes HTML files for your browser to read on the fly.

When you learn PHP and the WordPress functions and template tags, you can pretty much do anything you want to do inside your blog.  Change up the front page layout, add a search bar outside of the sidebar, set up different templates for different categories, and much more.

Other Themes

Ok, my secret to coding is this: look at other people’s code.  I grabbed some free themes and looked at how the author coded.  How he did this to generate that effect.  How she got that look for her text.  A book helps, but when you see it, change it, and learn how to tweak yourself, I think you learn faster.

I haven’t learned everything yet, not by a long shot.  If you have a tip or idea, leave a comment so we all can learn.