To revise for focus, you are looking at the Big Picture: what’s the main point you’re trying to make? Does everything connect to that one main point? How you work with focus depends on type of writer you are and the type of writing project or assignment. Those who write drafts much like free-writing (without much planning) probably need to step back once a draft is written and think about what the central point is: is it interesting to a reader? is it worth saying? You main point probably shouldn’t be some truism/cliche that everyone accepts, or it should tweak or twist that commonly accepted idea to get the reader to re-examine his or her assumptions.
Some types of writing (like memoir) lend themselves to with discovery drafts. In that case, you may have started with a question, a nagging itch: what did this event mean? how did this person influence me? You may not know the answer when you start out. If that was the case, then often you need to look back and see what you have discovered thorugh the writing. Look for the surprising statement that you may not have realized till you wrote it, but that suddenly seems powerfully true.
In a memoir, have you narrowed the time frame enough so that you can develop scenes?
With argument, we’re talking here about thesis. Some links:
On a smaller level, another issue to paragraph focus: does each of your paragraphs have one main idea?
Have you used topic sentences to establish those main ideas (when appropriate or useful)?