The better the mix, the less needs doing in the mastering stage. Always check your mixes in mono. Things can easily get drowned out when switching to mono.
You shouldn't be doing too much. As someone stated earlier, its bet to get someone else to master your own material because by the time it comes to that stage you've heard the track so many times, it sounds dull imo. A fresh set of ears can hear instantly what needs to be done.
My typical master chain will typically go:
Highpass filter (to shape the low end and roll off the real lows)
Compression to take a db or two off of the peaks (only if needed)
Multiband compression (if needed to help the bass gel)
Stereo width (I normally use the S1 from Waves, however I only use this if there isn't much width, i judge this by my ears and aid with meters)
midside eq (again only if needed, can be used as a replacement for the S1 if the track needs width)
Harmonic saturator (to help add depth, color, warmth)
Limiter (I aim to turn my track up till the loudest section RMS is sitting around 0dB in k14, the peaks of my track can fall wherever, as long as they are not clipping which is +14db in K14, however I'd normally aim for the peaks to be a few dB lower than this)
Most of mastering is just metering IMO. Check your phase correlation, stereo width & midside imaging, RMS & True Peaks meters. Learn to the K-System and when to use it. Don't squash your mix to aim for loudness, because you will lose punch. Loudness comes from dynamic range.
I recommend the Fab Filter Limiter, great for mastering in the box. Watch some videos on YouTube.
Mastering is just preparing the track for release and pressing
If you have any further questions, don't hesitate to ask. I've studied Music Technology at college for two years in the UK. I'm going to University in September and would like to share the knowledge I have learnt so far.