Layout: Study film, animation, and other comics. Look at every decision they make and try to figure out why they made that decision. Why did they frame a particular shot/panel the way they did, why did they put these two specific actions on the page, etc.
Read Scott McCloud's Understanding Comics and Making Comics (in that order). There are also a number of other books and online articles that cover this and other topics, look for them. I think we had a resource thread somewhere here that had a number of links...
Art: There are a million resources online, and they're a lot easier to find than comic-specific ones. Look for tutorials on expressions, body language, gesture drawing, simplification/exaggeration (stylisation), and, if you're not already good at it, anatomy. DeviantArt has had many good ones, but you could also look for Tumblr art resource master posts (google 'em), which work a bit like best-of compilations for resources from all over the place.
I'm not posting any specific links for three reasons:
1. Other people have already done a better job than I ever could of assembling links to great resources.
2. It's very important for you to know how to find resources on your areas of interest on your own, as a comic artist. Right now it's comic-making tips, in the future it might be costume and technology references for a particular era.
3. Different kinds of learners need different kinds of tips/resources/guidance. There are a lot of tutorials out there that I personally feel advocate terrible habits/practices, but they're immensely helpful to other people, and some tutorials that seem useless to some people have helped me a lot. It's best to do your own searching.
Pacing. Pacing is important to a story. If you make a scene end too quickly the reader looses interest. Plan out your story fully and layout every thing. I like to roughly lay out my story then I select the places I feel need to be build of dramatically. The size of your panels works the same way, the more gradually your panels increase in size, the more your reader is anticipating what is in the next one. Things like that smile
Hope this helped a little~