Hmmm. Good questions. Maybe I should bring this all into a small guide like I did on the "Starting with 20k" thread. But for now, let's see...
1) Trying to mix on bad monitors will not only drive you nuts, but doesn't do much to help your mixing skills. It is like spinning your wheels in a mud pit.
2) Bad D/A will also induce a mud-slingin', tire-spinnin', drive-you-crazy state of mind
3) Get 1 & 2 correct, then you have a golden foundation. You really can "hear" things in great monitors that you cannot hear in speakers you may love but are not intended for mixing.
4) No matter how much you think you can immitate the sound you love in speakers you know, it still will not do you much good if they are not flat studio monitors. If it is not clear by this point, get 1 & 2 right first.
5) Learn subtractive EQing. Basically, don't boost (only rarely). Instead, pull down the problem areas in the spectrum.
6) Speaking of the spectrum, I think a lot of live sound/monitor engineers get great practice learning how to mix because they have to be quick at notching out feedback and setting sound for a variety of environments. For example, that high-pitched squeal you might hear in a live concert is caused by a mic being too hot where certain frequencies are occurring. A live sound guy knows immediately to pull down 1.6k or 4k (just examples here) on the mains/monitors when they hear that frequency in the feedback.
7) If you don't have an opportunity to do live sound, then practice learning the 31 bands of frequency used in many band EQs. When you can hear them and name them by sonic recognition, then you will start to hear favorable/unfavorable aspects of recording gear.
8) #7 is very important
9) Reverb solves a lot, but can ruin everything. There really isn't an in-between state here. It is either DRY or SWIMMING if not done perfectly.
10) Don't turn knobs because you think you are supposed to.
11) Perhaps my favorite and the most eye-opening for me. When recording with less than stellar gear, there are a lot of adjustments that have to be made to get a good sound. This is obvious. But when using top-end gear - and this is what surprised me in a counterintuitive kind-of-way - a great mic+great A/D + great preamp + great cables = almost no EQ at all. The mic and the preamp define the color of the recording. The A/D conversion keeps the digital version of the sound on par with the analog version. The cables....well you just have to hear it. Good cables just bring the sound "here" rather than it being "there."
12) Learn bussing and submixing when it comes to trying to mix everything. This is typically a live sound engineer's skill, but it is important to know. In a live environment, most engineers get the sound they like once and can reuse the settings with only minor changes every now and then. The same can be said for your orchestral template.
13) When it comes to learning settings, there are basic settings for certain instruments and vocals that work 98% of the time regardless of the "brand instrument" etc. A kick drum should be compressed nearly identically to the next kick drum....etc. unless there is something specific you are trying to create that is outside of a normal mix.
14) Engineering/recording is an entirely different skill set than composition. It is boring when it comes to reading literature on it. But the characteristics of sound should certainly be explored. Nearly every engineer I've ever met has a copy of the most boring book in the world...otherwise known as "The Sound Reinforcement Handbook." Buy it. Learn to be okay with hating it. Then, suck it up, and read it all. Thank me later. I'm sure you'll curse me first...maybe for an agonizingly long time while trying to read through it. But we can high five after the Hallelujah moment happens.
15) Sound treatment. Know why it is important and how to use it effectively in both mixing and recording.
16) It is covered in the "Sound Reinforcment Handbook" but know the microphone types and why/how they are used in certain situations. Then, try it out on your own. Have mic shoot-outs, etc. Have fun with it all while you are learning. There is a tremendous amount of eye-opening moments to come from experiments like this.
That's about all I can think of for now (when starting out). But that is also a lot to take in. Ask away if you have questions. Hope this helps!