Have you ever mixed all day, thinking your track sounds great, only to come back the next day to realize your mix doesn't sound nearly as awesome as you thought? Do you constantly have to run out to your car to check the low end of your mix? If so, you should try using reference mixes. This is the one thing that made the biggest improvement in my mixes. It helps keep the finish line in site so you can be confident that the choices you're making are helping your mix and not hurting it.