Sometimes you need to get in really close to your subject and fill the frame with detail. But don't forget to leave space when it's needed. One of the most important times to remember this is when you're taking a portrait and your subject is looking to the side. Always leave nose room. You can crop behind the head as tight as you like, but make sure that your subject has some space in front of their face.
Take the above photo as another example. A tight shot would look good too, but this photo gives a great sense of how small and agile the aircraft is in the huge vast sky. So whatever your subject matter, the next time you're shooting something, why not zoom out or walk back and give your subject some space.