During the mixing process strive for the best sound you can get
without using any processors on the master bus,
Don't compress the mix.
Don't normalize the mix.
Try not to limit the mix.
Make sure there is no clipping - have your mix peak at around -3 dB . -6 dB
If possible, don't do fade-ins and fade-outs during mixing;
This can be done smoothly and easily in the mastering stage.