One of the most important things I learned on the job as a Senior Designer at MTV was: you don't have to reinvent the wheel every time. As a graphic designer, assembling a toolkit of brushes, textures, templates, and other elements is a crucial step to maximizing your design capabilities and efficiency. The other thing I learned was: you don't really have to know what you're doing! Thanks to thousands of readily available tutorials on the 'net, if you're not sure how to achieve a particular look or effect, all you have to do is google it. My favorite resource at the moment for tutorials and resources (including helpful posts like 50 Free UI and Web Design Wireframing Kits, Adobe Illustrator Tutorials – Best Of, and 40+ Excellent Freefonts For Professional Design) is Smashing Magazine. If you're a graphic designer you probably already know about Smashing, but if you're a filmmaker who also does some design -- and a lot of us do, these days -- check out the site (they also have a book).
Link: Smashing Magazine.