BURN YOUR HEADPHONES
First, you need to understand that when you use headphones for mixing audio you have to get a good pair and you have to get used to their sound. This is important if you wish to make constant quality mixes. The burn-in process is a technical thing you should do to fix the sound of your headphones. Once you burn them in, they will sound the same for the rest of their lives. This process usually takes about 100 hours of playback at moderate volumes. What happens with the drivers during that time? Drivers or capsules or headphones speakers are made of many different materials and use many different ways to produce sound. Let's say you have standard dynamic headphones. The speaker unit has a magnet, a coil, and a diaphragm. All this component has to be burned in. The diaphragm is usually made out of thin plastic and it has to get softer on the edges, to produce low frequencies. Why softer? So it can move easily back and forward. The sound of your headphones will change for the better in this period. They will lose the harshness, that almost any good pair of headphones have, when you purchase them, and they'll get more natural overall sound.
How to burn in your mixing headphones?
There's more than one way but to keep this simple. Plug your headphones into any device that you can miss for a week. Any old hi-fi stereo system will do the job. Just plug the headphones and turn the volume to moderate levels and leave it on your favorite station for a week. You can check the progress in the meantime if you feel like it or wait for the aha moment after you hear them after a week of burn-in process. That's it on the simple side.