Great point-outs here.
I'd like to add the importance of mixing at a moderate volume on your speakers, and referencing your mix to other mixes to keep your feet on the ground.
Also proper gainstaging and leaving enough headroom in the mixertracks and other elements (this won't dramatically change the quality of your mixes and take it to the next level, but it will hopefully make the job a lot easier since you get "more space to play with" and can do the moves you couldn't do if you had horrible gainstaging).
Get to know your tools and techniques so you can have it in the back of your head, so you don't have to struggle with a new technical issue each time, and can focus on the balancing.
As Nutek stated, work at the samplerate you want to work at. Some people want as much samples as possible, while some thinks less is more (Dave Pensado for example prefer mixing at either 48 kHz or 44.1 kHz).