Do you always wack compression over your master outs?
To get the music pumping either a little or a lot - but that depends on the program material.. dont always use a compressor and the settings are usually mild.

Especially if you intend for your music to be placed on vinyl.
That'd be nice, but i dont have the money (yet)

All your doing is sacrificing headroom and dynamics for apparent loudness.
and the final "loudness" of your tune bears little relation to how loud it will be on vinyl after the mastering cut.
Can you elaborate more please? What would really display this steve would be if you posted up a pre-vinyl track and a recording from the vinyl.. in wav format please so we can see the difference...?

Only use mastering compression if you REALLY understand compression, because you are going to make things very difficult for the mastering or cutting engineer if you don`t, and may end up with a flat, squashed, thin sounding record.
People have to start somewhere and compression as a whole concept is difficult for people to hear in the beginning, because they need to train their ears. But mastering compression is different - its true.

And for gods sake, if you don`t really understand compression at the mastering stage too well, then don`t for any reason use MultiBand compression.
Thats a good point.

This is a very specialised form of compression, and is generally only used for very specific surgical tasks.
Its difficult to convince people of this, esp when the preset from a Multi-B comp makes things sound louder, better and fatter.

Try to leave your final mixdown with a good 3db of headroom (or cushioning) from peak level to 0db if you can.
the amount of artists ive seen ram their music all the way up is unreal

Yes your tune will apparently sound quiter (ever heard of a volume knob?), but the spared dynamic headroom will leave more room for play for the cutting engineer or mastering stage, and will leave a far better sounding audio piece.
Indeed.

The same can apply for EQ and any other effect you place over the master.

If you are applying the same effects over the master channels of all your tunes (and applying similar settings each time) then you are effectively putting a standardised template over all your music (which from tune to tune will not be standardised, and will require different or NO application of mastering techniques each time).
THIS IS VERY BAD PRACTICE!!!!
Indeed.

Think before you apply mastering effects.
then think again.
Do you REALLY understand what you are doing?
Actually, there is something to add here -

Do you need to master.. AT ALL? A good mixdown will mean that the mastering really is more like a french polish.