I recently became a director of sketch comedy videos for the Upright Citizen's Brigade website, UCBComedy.com
Here's a video I directed and did the effects for recently.
Some people asked me how I created the backgrounds for the video, so I figured I'd go over the basics.
In Photoshop I start with flat colors. I try to go with a middle color for each section, that way I can add shadows and highlights later.
Then I add extra layers on top of darker colors to create shadows. It's pretty common for me to use 3 or 4 layers per section to build up shadows gradually, instead of trying to do it all at once. I use different opacities and blending modes on the layers to get the look I want.
Next I do the same thing, but with highlights.
This still looks very computery, so the next step is to overlay photos of textures to get the types of variation in color and value that make something look real. For the wood I added some wood textures (a no-brainer), and for the glass I added some concrete textures to make it look frosted.
And finally I flattened the glass section and warped it a bit to make it look curved instead of flat. In general, it's much easier to work with rectangular shapes (because it's much easier to make rectangular selections), and then when you're done, warp them into the shape you want.
And just to give you an idea, here's a screen capture of just some of the layering that went into making this background.