My personal opinion about music is that it is very powerful and usually has quite an effect on your thoughts and feelings.
23 And so it was, whenever the spirit from God was upon Saul, that David would take a harp and play it with his hand. Then Saul would become refreshed and well, and the distressing spirit would depart from him. 1 Samuel 16:23
Therefore, for me, my guidelines are:
First and foremost, the lyrics must be words I’d feel comfortable having Jesus listen to with me. I don’t believe in the “I just like the music… I’m not listening to the words” thing. :P Often, when we subconsciously listen to something, it has a way of going deeper into our minds.
Secondly, I listen to music that has a positive effect on my moods and thoughts. If I listen to music and feel uplifted, joyful, thankful to God, ready to clean up :), etc… then I will listen to it again.
That’s pretty much it. I used to think that “loud music” was bad or something, but now, after reading the Psalms, I don’t think their music was very quiet.
3 Praise Him with the sound of the trumpet; Praise Him with the lute and harp! 4 Praise Him with the timbrel and dance; Praise Him with stringed instruments and flutes! 5 Praise Him with loud cymbals; Praise Him with clashing cymbals! Psalm 150:3-5