The best source for learning how to develop a theme is the WordPress Codex. I could copy and paste it all here, or you can go check it out. It's all here and very clearly laid out WordPress Lessons « WordPress Codex

Start with a framework, and learn how to customize it.

Use the Twenty-Twelve or Twenty-Thirteen theme as a framework, build a child theme on it.

Child Themes « WordPress Codex

You'll get a feel for how a theme is put together, and by using Child themes, your theme will stay up to date and secure whenever Wordpress updates the parent theme.

You can also build child themes on ANY theme, so you can get a framework like Genesis or Bootstrap, and build custom themes on top of that.

Start by making small changes in your child theme, and move forward from there. Post specific questions here, I'm sure you'll get good advice, the more specific the question is.

Hi
You can see this link
WordPress Theme Development Training Wheels | Wptuts+

Yeah don't reinvent the wheel, start with a Wordpress theme framework, like this: Hybrid Core WordPress theme framework Or this: Underscores | A Starter Theme for WordPress

Note that a framework is not usable on its own, it is only a starting point for you to build a parent theme.

The last time I created a Wordpress theme it was more "turning my current HTML site" into a dynamic Wordpress theme. This video series seriously helped me out:

https://www.youtube.com/watch?v=8EDJfrD_G8A

There are like 5-6 videos -- each of which are like 24 minutes long.

Even if you're looking to do more than just this, you might find some decent information from the series above.