Regarding practice, I recommend you try drawing or rather recreating the things you like. If you want to draw dogs, look up pictures of dogs and try to get your drawing to resemble the reference as close as you can. Try to keep up a habit of doing this every day, if only for a half hour at least. If you're not feeling up to it, just know that idle doodles on the back of your textbooks are better than not drawing at all.
Regarding, theory, my suggestion would be to pick up Keys to Drawing by Bert Dodson. It's a dry read, but that will clear up any misconceptions about drawing you may have, as well as presenting you the proper mindset to approach the craft. The exercises in it will also hammer symbol drawing out of you and teach to you to draw what you see over what you think you see. Afterwards you can approach any subject you like with confidence.
Something else you could try is looking up drawing process videos. Pay attention to what they do and try it out yourself.
Uh, this is a nice bookmark to have, too.
http://endling.deviantart.com/journal/I ... -219754628 give it a read sometime
and uh, if it adds any worth to what I'm saying, here's some of my work