Download their very basic theme which is twenty ten and learn from it. BAsically, what you need is an awesome design with a powerful framework.
You can manually code it from scratch if you wish. The main files a wordpress template needs is index.php and style.css with the appropriate header. The rest of the files are use to describe the layout of specific type of pages and to add functionality. You design the theme using graphic software like Photoshop and slice the images out to use them.
If you want really good worpress theme will find good design and order design what you think will be better for you. After find the programmer. Or find some interesting wordpress theme and a little customize it.
Download the free sample wordpress that closer to your design, and modify from there. It will be much more easier rather from scratch.
I think you should try creating a beautiful wordpress theme in photoshop- Here is the link for guiding you- http://nikhilmisal.com/how-to-create-beautiful-minimalist-wordpress-theme-in-photoshop/ Hope it will help you.