Monitoring is a critical factor, probably the most critical factor, to making good recordings. Lots of info on the site if you search. Listening to your tracks on a wide variety of systems tells you a lot - car, home stereo, studio monitors, iPod earbuds, etc. And using reference recordings - pro recordings that you like the sound of and that are similar to what you're going for - to compare your own to on those same playback systems. It takes a lot of work to get to really know your monitor system, and get it set up right. Well set up speaker systems are better than headphones for accurate monitoring of sound quality, IME.