Depends on what you are going for but I tend to think guys look the best with the hair cut as short on top as can be done with scissors. Then shave the sides with a 3 and blend. Then style the hair with some gel or something on the top, usually part on the left or right side, never in the middle. This works for me when in "guy" mode pretty well. Took me forever to figure this out, but of course, different things work for different people.
This is just my personal opinion, but I think the trick is to get it as short as possible while still allowing you to style it. I look at a lot of guy cuts and what I notice is the mistake a lot of them make is to cut it either too short for any style, too long to have what looks like a clean style, a bad style, or part is just not correct.