I was told that my greatest setback in my comic is the lack of backgrounds. I have addressed that issue using a very useful technique I found online that was used back in the days of animation. It's quite simple actually especially when you colour digitally. You draw the background and actual comic as two separate things. Plus, after you scan your pictures, make them transparent so you can put your background underneath the panel. This way, you can reuse the same background at multiple angles, sections and colours especially if you're using the same scene over and over again. Making your backgrounds takes time, but once you have them, they will save you a lot of time.
Yeah, layers are pretty awesome, aren't they? If you aren't already, I'd strongly suggest using different layers for dialogue, SFX, and components of your characters, too--in my comic template I have seven to start out with ("matte", "fill", eyes, eye details, gradients, shading, ink). This is simplified, with my pin-ups I use significantly more, and I'm sure more experienced creators have additional specific layers that they can't live without.
Here's a couple useful tidbits I've got on backgrounds:
I tried to do this once but later on it became more of a hindrance. It might work if your scenes had little variety of shots but I found I had to keep throwing the backgrounds out and drawing a new one anyway because I don't like to have side on, eye level shots all the time.
Layers enable me to move way way faster on ‘simple’ art because I can be sloppy with my lineart.
Case in point, drawing a staff held in a hand—instead of having to carefully trace the construction lines on both sides of the hand to make sure they line up, I create a new layer and have the lines for the object on one side carry over to the other side. Then I can erase the overlap with no consequences before merging layers.
Multiply and crop to layer below are also huge time savers. I strongly encourage learning and employing them.
Edit: “inverse fill” is my latest favorite—try selecting all the non-characters white space, use the “inverse” function, and then paint bucket everything. I’m screwing up the vocabulary, but this trick saves me so much time and “white pixel” correction..,
Backgrounds, like everything else in art, are a wild beast all on their own, a separate discipline that helps to form the greater whole, and sometimes even moreso than the characters require special thought on what you're showing, for the reasons of drawing the eye and saving time.
Backgrounds are most-often constructed in three parts: The background, middle-ground, and foreground. Including all three elements but keeping them distinct adds a richness to the visuals.
Each of these elements need not be overly complex, though. Here we have the background(a wall with a simple pattern), the middle-ground(the floor and door to the left), and the foreground(mixed silhouettes of ruin). The details on all of these things is moderate at best, but it's fairly easy to get an idea of what kind of environment they're in.
It can also be important to remember that the boldness and brightness of the colors has an impact on what it is the viewer pays attention to. I shaded the characters in black so that they would stand out from the more neutral surroundings. Various colors are read as "more important" than others to the human eye, with blacks, whites, and bold yellows and reds being most visually distracting, with neutral browns, grays, and green-blue-grays being the least distracting.
Note that this is less important the longer the characters stay in the same scenery. When you go from masters(establishing shots) to coverage(closer views for the purpose of dialogue) you can simplify things further, pulling out and/or changing angle every so often for visual interest. That may require more details briefly just to remind the viewer what's going on.
You can also use the scenery to draw the eye in various ways. The lines of objects in the scene, as well as their brightness/boldness will direct the eye like arrows and signposts, so you could for example have jagged rocks or tree roots that point toward important aspects of the scene, with those same points of interest highlighted slightly behind them by clouds, bright & bare building faces, featureless rocks, areas of less detail or more detail, and so on. Contrast is the key. Find ways to save yourself time and effort for the viewer by using details strategically.
I've also seen in other webcomics and official media that they make use of 3d rendering stuff like google sketchup. In fact, Ken Akamatsu from Negima and the guy who makes Gantz uses the software just so they can have backgrounds they can re-use.
And the crazy thing is, those two men have come up with a way to make the 3d rendered stuff not look out of place.