Having a mixing goal - Dont be afraid to start again.
After over 10 years of mixing and mastering professionally, I've added a lot of skills to my arsenal that enable me to achieve the mix I set out to get from the outset. There are the obvious basics and of course, and more of the 'black belt' stuff that I employ to get what I want, but theres also a big one that often gets overlooked, and that is the ability to recognise when your heading off course!
If you you ever find yourself filling up all your inserts with plug ins with an idea that 'one more will make it right', then there is a chance that you strayed too far from your intentions and now you're trying to cover your tracks. (no pun intended).
In this situation I have found that simply starting again from scratch can give you a totally different perspective of the mix and enable you to approach it from a more informed position, as Thomas Edison once said 'I have not failed. I've just found 10,000 ways that won't work'. Hopefully you wont be doing this 10, 0000 times of course but the act of starting a again means you have the benefit of knowing what went wrong the first time.
I first learned this in the early days of mixing on unstable computers that would continually crash. Losing hours of what I thought was my best 'genius' mixing, I would begrudgingly have to start again thinking it couldn't possibly be as good the second time and then subsequently realising that not only was it faster the second time, but that it was also noticeably better!
After this I was able to use this to great affect by first checking my ego by the fact that I hadn't done so well at achieving what I wanted, and then simply starting again. Remember you haven't lost any time and you could be saving way more than realise by getting yourself out of mixing cul-de-sac that you didn't know you'd even put yourself in.