In difference from any random CMS system, webshops in general and Magento in particular needs soo many components in the right place to work in the front-end.
I’d recommend to find an as minimalistic theme as possible (i believe there is one called “blank") and start experimenting with that.
I started with Magento last summer and i did not found any great articles/tutorial/resources. I even read a book about theme designing, but all that stuff is very basic. It took me some months of daily work to feel confident of what i was doing. And that came from experimenting and googling particular issues as i stumbled upon them, since they are often covered in forum and blogposts somewhere.