Making these half-pagers is usually a balance between providing exciting art for the client and planning where to put your efforts to maximize the results in a short time frame. Often an art order can be 5 images requested on a relatively short deadline, so you need to have certain tools and tricks to get the job done fast. I happen to have a very literal, rendered style at the moment, so I'm constantly employing 3-d models and other bits of reference to get the perspectives and realism needed for a consistent level of detail.
Below we see a quick 3-d modeled "set" that gives me the correct perspective and lighting for this multi-tiered fighting platform. This may take an hour or so to build in the computer, but its way faster and more accurate than trying to draft the structure out in pencil.
The structure is then worked into the drawing of the 2 characters fighting.
Similarly below, I've got a character running at us drawn without reference just using comic book construction techniques. Since he's mostly clothed, I just need some information to flesh the head structure out at this angle...
Which is obtained by holding up a foam planar head model and snapping a quick photo. It just worked out the character was bald and fairly generic anyways, so my foam head does the trick nicely.
If you've got a more graphic, cartoony or otherwise efficient style, I salute you. If you're like me and have to "get it right", then employ whatever tricks you need to get the job done as a professional in your allotted timeframe.