Tutsplus has a great guide to Web Design Theory that I recommend.
I also went through several of their Illustrator tutorials just to familiarize myself with Adobe Illustrator and vector graphics editors. These will at least help with the mechanical part of designing logos.
The creative part is another realm unto itself that's hard to teach. A lot of design curricula will start off with drawing course. So I would recommend practicing drawing everyday. Drawing is usually where an idea for logos would start.