Music is very important in life. People use music for various music reasons. I often find myself listening to particular songs in preparation to doing battle for something. For example, before the CH302 final, I distinctly remember listening to a particular eurobeat song over and over at almost 80% volume. Eurobeat kicks ass in that aspect of pumping me up for a test, but also increasing stress, really eustress, the kind that is probably responsible for most of my grades.
It would be appropriate to think of my mind as some kind of large maelstrom. Listening to Eurobeat only adds angular momentum to this storm, making me hyped before the test. I then take the test, effectively high off this added energy. The only after effect is that when the test is over, I think to myself - What the hell just happened? I then obsess over my performance.
Other times call for different tunes. For example, before my interviews, I need to decrease stress levels, so I usually listen to something very structured like Bach's Brandenburg Concerto No. 3 (Allegro). I find it neither pessimistic nor optimistic, just confident. The kind of music that should be played (before and during) when fate executes its will.
Nevertheless, some classical music actually increases stress. Tchaikovsky's Swan Lake has this effect. Try listening to it at a moderately high volume. I feel really messed up inside when the forte part starts, like there is no justice in the world. It's winter break, and I feel panicked for no reason when this one shuffles around. Other songs can actually almost make people cry - (Waltz of the Flowers, etc.)
Even then, music doesn't always cut it. The day before my last MCAT, I spent almost 2 hours looking at pictures of airplanes and videos of takeoffs/landings. This works wonders.
Pop music on the other hand, is meant to be extremely catchy. I do not recommend ever using pop music for any reason other than finding ways to ridicule _______ (insert your favorite band here), although there are exceptions.
The catchiness of pop music will cause problems. Inadvertently, certain phrases will be stuck in your head, which will repeat endlessly. That being said, Maroon 5's "It won't be soon before long" is an awesome album. So is "Songs About Jane". Please let me join you, Maroon 5, as chief entertainer.
In any case, find something that suits you. Just don't start making music (unless you're really good at it) i.e. don't turn into a damned hippie. Playing pre-written songs and calling yourself a 'band' doesn't make you musicians, rather, cheap emulators. My $100 speakers can do better than your $1000 set of instruments.