Just to add my 2p.  Assuming you're happy with the actual mix, you probably need to do some basic mastering.  I'd suggest you start with some EQ to get rid of any harshness. Or even better, a multiband comp.  Then go into a limiter (or even better, just use a multiband limiter)

e.g. Waves C4 into L1

or L3 Multimaximizer)

or iZotope Ozone - dial in one of the presets till it sounds good - tweak as necessary.

I would also suggest TT Dynamic Range Meter to keep an eye on the dynamic range and X-ISM to make sure you don't have any intersample clips (although Ozone is supposed to warn of this)

Make sure you experiement lots and listen to reference material often

Compress and then limit on a master fader.

record in 24 bit and super low becomes super high anyway

"super low" is just as bad.
you have a limited bit depth, make the most of it

and kids thats why we record everything at super low volumes...when almost all peaks are over 0db it sounds like garbage

It takes the highest peak and raises the volume of the track.
The highest peak becomes 0dB

An easy thing to do if you have a bunch of finished, mixed down tracks (say for an EP or something) is to import all the tracks into your DAW in one project/file/whatever so you can listen to them all side-by-side and even out the volume between them by ear.

Thank you! Someone finally mentioned psycho-acoustics. Higher pitched sounds usually sound louder than lower pitched sounds, even if your VU meter says they're the same. In my experience certain timbres also seem to sound louder, even at much lower volumes. They seem to cut through the mix. Masking is another weird phenomenon you'll experience in mixing. Cymbals and other sizzley, white-noisey sounds can tend to mask certain lower pitched instruments and frequencies if they're up too loud in the mix.

Oh okay. That's cool. And going through them myself does make sense. I'll do that too. Thanks egr!

Well, a compressor actually changes the relationship of the peaks in the waveform.  Normalize does not, it just raises everything together equally.  It's just a "volume knob" really.

The best thing you can do is just adjust all the track volumes by ear.  That's what you're actually going for... for all the tracks to be perceived by a human ear as having the same volume.  That is not the same thing as having identical peak heights in a waveform.

So it's kind of like a compressor?

Normalize just amplifies the sound until the highest peak hits 0dB (or whatever level you set it for).  If you already have peaks that high in your recording it won't do anything at all.

You can. What does that do though? Haha, I've never used it.

you can 'normalize' in audacity, right?  i've got a super old version on my computer...  you can in it at least.   i'd assume the newer versions as well, probably with more parameters.