I will EQ every channel. You could talk forever about EQing different kinds of sounds, but for me the most important thing is keeping the low end as clear as possible for the bass and kick drum.
Every track will have a high pass filter applied. I move the frequency up until the sound starts to lose some of the quality of sound i like it in. Usually you can take a fair bit off the bottom without it sounding any different at all. Usually you can position the cuttoff point just below the 'root frequency' if it is a sound with a clear note. I will do this solod and again perhaps with the whole mix, as often you can take even more off when it is part of an ensemble. This kind of treatment of everything can free up a few db of DB of headroom, bring up your overall volume, and make everything sound more crisp and less muddy in the low end.
If a sound has a 'solo' bit or sits in a breakdown where it needs to be EQd less heavily, then you can automate your settings so it can take up more of the spectrum in these bits
i do agree with HPF cutting the low bass on the majority of tracks, however i think it depends on how many layers your track has. if you have multiple parts all shouting for space then yes, which is quite common in psychill, psy trance etc and cutting most of the bass of those multiple tracks may well be the best option. It's also quite useful if you are recording a lot of live instruments as the micing up procedure can introduce a lot of noise in the lower registers.
however as iacchus says, in intros and breakdowns (using automation if you need to, (or bounce an audio un-eq'd copy), yes it's often better to leave the full spectrum of the sound. or in drone ambient music, let the fullness of the sound flow out. (Although with highly reverberated sounds you have to get very surgical with the eq's on the reverbs).
But consider a moment a track that is somewhere in between pure atmospherics and a full on complicated track with multiple parts. A simple track structure i.e. a drum part and bass line with only a few elements on top at any one time.
In such instances sometimes you can be better off sometimes leaving the fullness of the sound on the musical parts or only doing a minor HPF cut on the subs up to 30hz. If you cut unnessarily you might end up thinning out the sound a little too much and then you feel like you need to keep adding elements to fill the track out, which ruins your nice simple track structure. Sometimes the lower freqs only muddy up the mix, sometimes they add body. Depends on the sound and the track I find.
So I try to work out what the core elements of any track are and mix that part of the track first. ie there might be a recurring pad or rythmic sample and I get those parts all sorted and eq'ed in tandem with the drums and bass.... then kind of fit everything else around that.
My advice would be to hold all the advice you receive and to apply it according to your track. Like Iacchus said, you can;t be too specific about what eq to use on what instrument and where....as it really is a case by case basis.
If I was going to add any eq to the master I would would probably do a very small bump at 80hz and a very slow rise from 1khz upwards.
This might be useful to help you get a vibe going on a track as it will add a little zing to the proceedings, and the eq on the master does tie the sound together. However I think you're really better off doing this type of eq'ing on your groups bus, the drum bus being perhaps the most important part.
I can recommend Pultec Eq's for adding a very nice crisp but warm upper range and deep warm low end. UAD do a version but there is also a free version on the Computer Music magazine DVD which is also very good.
I would also add to be careful of using presets on some synths as they are designed to sound impressive and sell the synth (i.e. a very big broad spectrum sound with tones of distortion and eq boosts and delay that try to draw your attention towhat a wonderfully clever synth you are using). These sounds can sometimes eat up your mix and you have to get very tough with the eq-ing. So check within the sound structure of the preset to see if you can cut eq or distortion anywhere.