Theme Development Training?

Hi. I’m self-taught developing websites, primarily wordpress, and have a basic understanding but I hope to actually know what I’m doing one day.

I’d really like to hear from anyone who has some advice about the best path for learning web development quickly and effectively. I can’t do full-time university program at this point, I just want to understand code well enough to create better sites and ultimately create my own themes.

Anyone have some suggestions/options for classes, on-line training, workshops, etc? Thanks in advance for any help you can offer.