I'm not Bob Katz, but... Here's my $0.02:
Most importantly, get the best monitors you can afford and get your listening setup as dialed in as you can. That's all pretty relative to your particular situation so I'll leave it at that. If you have a decent D/A converter (say, an Audiophile 2496) that's a good enough starting point. You'll get more bang for the buck with better speakers.
Next, as someone who's getting more serious about mastering, I'd say that the biggest learning curve for me was (and still is) to learn how to balance my masters against other recordings on different systems, since I don't have a perfectly tuned listening room by any means.
That means getting really familiar with the characteristics of a few listening environments (monitors, car, home stereo, headphones) and how some specific source material translates across those environments. The source material should maybe represent some extremes as well as some nice balanced recordings.
The point being, what you're working on is never gonna sound exactly like anything else, so don't even bother with that. Just try to make it sound nice and balanced on a few different systems using other records as guidelines. Like if you know one album is particularly bright overall, use that for reference as your absolute limit for high end and back off your high end if you're getting too close.
Now for loudness... Same as with tonal balance, you're not going to get your stuff as loud as some records that are out there, nor should you want to. The loudness is totally relative (to the volume knob for starters) and the really "loud" records ironically end up sounding worse when you play them loud, and more often than not sound like total shit on good speakers at any volume.
The real power of a recording comes from the material, performances, tracking, and mixing. If you have a good mix, the mastering should just flatter it -- glue it all together, and give it some boost while respecting the intentions of the mix (if it's already good, don't fuck with it too much). It's obvious enough, but your master will generally be as good (and as loud) as what you're given to work with will allow.
Now having said that, of course you're going to try and make it loud. Shit, who are we kidding? Try to find the point where you're starting to sacrifice tone and dynamics and back it off a bit.
For processing you'll need a good compressor, broadband eq, and a limiter to start with. Absolutely, do not try to go crazy with a multi-band comp or a stereo imager right away, you'll spend lots of time making things worse.
Use a broadband comp and learn how threshold, attack, and release can affect a whole mix first. You probably want to stick with a low ratio in general. The broadband eq should be used sparingly to remove some mud or whatever. Try to cut rather than boost, of course. The limiter should prevent "over zero" clipping and dither (if necessary) as the last step. Use it to level off the dynamics of your recording so that it's consistent. Try to find the right threshold where you're slightly, but regularly reducing the peaks, which should mostly be snare hits.
Holy crap. Ok, I'll shut up now. /SPIEL