It's not really a thing about cropping for the most part, as what you have is just text with a gray background. :)
Give yourself your work area first, so you know what you have to work with. Think of something with a little more width, but a little less height. Taking what you currently have, perhaps drop the height by 1/4, and extend the sides by 1/4. That will give you a nice banner.
I figured I would show you what I mean, so I did a quick reorganization for you that cuts down on the open space while still keeping a similar design. As you can see, it would fit into a signature very well, and it won't take up an entire screen :D It took me a whole 2 minutes in MS Paint, so just by going into it with an idea, and the knowledge of how much space you have to work with, it doesn't require much know-how or skill at all. All you need to do is add your background first, then the text, and (if the background is the same color throughout) you can just use the select tool and move things around at will, and the eye dropper and paint bucket to fill in any open patches caused by the select tool!
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