Skip to the last line for the pearl of wisdom amongst my waffling.
I use the spectograph-wotsit to help visualize any problem areas in a mix. Particularly with individual instruments solo’d.
Its particularly useful to see which tracks are muddying up the bass end.
And to throw in my opinion on the matter of eq pattern cloning, now is probably the best time in the history of recordings not to sound commercial, cos the big labels aren’t doing that well nowadays are they?
OK… now then, a pint of the finest contintental lagers worth mixing/mastering tips.
With nearfield stereo monitor speakers, your head and speakers should make an equalateral triangle. You ears should be in the same plane as the speakers… or angle your speakers up or down to point at your ears. or raise your chair/stand up/sit down get speaker brackets… whatever.
Dont master with tired ears. Also dont mix down with tired ears.
Do your final mixdown on a day when you haven’t been composing. I appreciate volume helps get you into the groove. This tires your ears.
If you’re working on a project of numerous tracks you really ought to master them together. Not weeks apart in between writing for the project. This will make your life easier when making decisions for each track. Master tracks at the end.
When mixing/mastering, you’re doing it too loud if you cant converse with someone in the same room. Your ears will tire quickly and then you are wasting your time. You’re probably damaging your ears too.
The ears perception of bass, mids and trebles change the louder you monitor. I might have it the wrong way round- but im quite sure your ears become less sensitive to bass at higher volumes, -of course experience can correct this phenonomen.
When your at a concert/festival, look at the well paid sound engineer- he will be double checking things sound ok through his/her expensive soundproof monitoring headphones. Headphones are also great late at night.
Unless your vey lucky, your room will be full of reflections and standing waves. Louder volumes make louder reflections and at certain energy levels walls and furniture will start to resonate creating more noises to confuse you.
These noises and standing waves will create holes or increases of volume at certain frequencies in your room. (refer to headphones)
Bass traps and sound absorbing panels make a real difference to problem rooms.
Make one cheaply from a rockwool panel covered in cloth so its not itchy. A wooden frame around it will help it survive being moved.
Put it on the wall opposite your speakers.
(When tracking vocals, stand in front of this panel facing away from it- for double value for money).
The mastering stage generally requires a touch of eq, some compression/limiting and maybe narrow the stereo field in the low end. -although this narrowing is better done within the mix rather than across the final mix (-artifacts).
Dry minimalist mixes may benefit from a sprinkle of best quality Reverb across the Whole mix.
Also… reverbs can mud up the mix. Make sure you keep an ear on any reverbs’ bass end. (put a filter or eq on the reverbs buss)
I stear clear of using multiband compressors and enhancers across a whole mix, unless you have a very expensive wonder-master-finalizer-pro MkII © The rest of them just sound good to tired ears by exciting certain frequencies.
(EQing/multiband compression or filters can create a phase shift. you generally want very little phase shift across a mixdown)
Use multiband compressors/enhancers on buss groups or individual instruments where necessary.
(if you use on across the whole mix, being sparing with its settings will be alright)
If you have excessive stereo bass/kicks and your tune ever makes it onto vinyl the needle will jump out the groove… unless the cutting house adds even more mastering. Also a panned kick in a night club with a central sub-woofer may sound rather shit… you’ll hear the kicks attack to the left or right, and then a delayed whoompf in the middle.
If you need to massively change the EQ at mastering stage, you fucked up when mixing. Probably cos you monitored to loudly or your ears were tired. -Try mixing it again another day.
Once you have mastered, double check that it sounds ok through a teenagers’ mobile-phone loudspeaker setting.
However, if you got something sounding good, i’d fuck the rules/guides and go with it.
And Probably best you dont take it all too seriously cos the experts tend to be boring. 
I may have missed one or two things.
Of course most guides and rules of thumb can be absorbed or ignored but…
------------don’t monitor to loudly------------ (apologies for not really answering the question)
