If you are not likable don't do away rotation.
It your application looks very good on paper and you are likable, an away rotation won't help you unless it is MGH or UCSF or a very competitive program.
If your application is mediocre or weak, an away rotation can help you a lot if you are personable. If you are not personable, then it will definitely hurt you.
Don't make anybody angry even a first year resident or a tech. This will hurt you a lot. Be friendly, but also be professional. Don't tell people about crazy things you've done in college. Try to be helpful but don't overdo. If they don't need your help, don't push. The only way to help people in radiology is to review patient's chart, history and ... Don't think that you can help people by telling them the imaging findings. Ask questions. But if they are busy, don't interrupt the workflow. If they ask you to leave, please leave. They are probably very busy and want to get things done on their own. Don't push to stay. NEVER EVER correct a resident even if he makes lots of mistakes unless an attending asks you. You may think you can shine by telling something that a resident does not know. Believe me. It does not help. You may think it helps. But no. Even if you are correct, at most people will think that by chance you know something or you have heard it from someone else. But you will make enemies. During interview season, all PDs will ask from residents about their experience with medical students and this can hurt you.
In one line: During an away rotation, nobody is going to be impressed by your knowledge in radiology. There is no such thing as "magic good eye" or "born to become a radiologist". People mostly evaluate your personality and your character.