No matter what you're writing, you should always have a grasp on the reason you're doing it. This keeps you focused and on point.

Is your objective to provide a step-by-step, systematic guide to accomplishing some task? Then the only thing that's really important is outlining the steps, along with enough information to give it context. Too much explanation bogs down the reader and can bury the point you're trying to make, lessening its impact.