I always make sure I have as high kbps rate as possible. I had a Rammstein track with 128 kbps and it sounded bad. Then I got another file with the same song with a bit rate of 192 kbps, and it sounded much better.

Also, when I transfered music files from WMP to my mp3 player, WMP compressed the music files. They sounded worse after compression; not as clear as the uncompressed ones.