While you have some awesome advice , mine would be just through a limiter on your mix to the desired Rms level
and leave it ,  if you have a good monitoring system you will have a decent final product.
   if you are just learning about mastering , you are more likely to mess it up than enhance the song.
     but that would not be as much fun , would it :)

So how do I export the wav directly from the master bus rather than exporting all tracks together? Thanks!

I'm sure others have given better advice...but
Have a linear phase EQ at the ready...
Get a nice slow lazy compressor to shave off a couple of dbs's.
Set your limiter to -.3 Peak, and aim for -12 RMS.
That's a simple formula to start with.
 
There's really no simple way as others have said, but that's my attempt at a simple way of doing it.

johndavidross
So how do I export the wav directly from the master bus rather than exporting all tracks together? Thanks!

That option should be a preset when you go to export audio files. (I'm not at my daw at the moment or I would tell you what it's called exactly).

I found a great series of tutorials at http://prosoundformula.com.  The guy provides some excellent intros to mixing and mastering, and the latter I found particularly useful.  I ended up building a mastering template in Sonar based on his workflow and it absolutely made a big difference.  Sign up is free, and there's no subsequent sales push.
 
If you are unsure where to start, and what to apply where and why, I can highly recommend this series.

Personally, I am a visual learner.  If I can watch someone do something, I can learn to imitate it.  About 6 months ago I watched a You Tube video of Ian Shepherd mastering a pop song.  In about 30 minutes I was knocked out by this man's ability to show his workflow with such excellence to achieve the end result.  However, because I watched someone who is far greater than I, there is something now that I can try to imitate.  But when you watch someone who is excellent, they make it look easy.  You'll never become a better tennis player by playing an opponent worse that you.  Learn from those who are highly skilled.  What are they listening for, and how do they make what's there better?  It is an amazing craft to learn.  We're all on the same road.

johndavidross
So how do I export the wav directly from the master bus rather than exporting all tracks together? Thanks!

If you're talking about simply selecting one track to export while ignoring all the other tracks, just click on its track number and it will get highlighted.  When you now export, only that track is exported.   Likewise, you can manually select individual tracks in the same way.     Hope that's what you were asking?

Okay, I have been playing around with everyone's suggestions. Here is an acoustic version of one of my band's songs. Let me know what you guys think. Thanks!
 
https://soundcloud.com/jo...k-mix-4-master/s-BqefM

johndavidross
Okay, I have been playing around with everyone's suggestions. Here is an acoustic version of one of my band's songs. Let me know what you guys think. Thanks!
 
https://soundcloud.com/jo...k-mix-4-master/s-BqefM

There is a songs forum here where you may get more comprehensive advice/comments.

All in all not a bad job.