final mix volume

I've tried searching these forums for similar subjects, but I just can't find the answers I'm looking for.
I am trying to understand how to increase the volume of my exported audio files to something close to what you hear on commercially produced CD's. When I play my song through an ipod or stereo system it is not even close to the same volume as other music. I pretty happy with the final mix i have come up with but the volume just isn't there.
Can someone help explain this to me and what I can do to increase the volume?
Thanks,
John

Hi Greg, thanks for the quick reply. Here's some info about what I have done so far.
I have three midi tracks (bass, drums, keyboard) all using soft synths (Dreamstation and CW TTS-1). I have three audio guitar tracks. I have the three audio tracks going to an audio subgroup where I am applying some effects to the whole group. Then I have the audio subgroup and all the midi tracks going to the master. I have the Sonitus EQ and compression applied in various places, mostly by trial and error, trying to find out what works. If you are interested, you can hear what I have come up with here http://soundcloud.com/johnrwillis/you-made-my-day-102511.
You ask about buses, I am not sure I really understand about those, is the audio subgroup a bus? Not really sure how to use these.
Thanks again for you help, if you have any advice or tips on my song I'd be interested in hearing from you about that.
John

Here's what I do...right or wrong... this is how I do it on every song I complete. My final levels on the songs compare favorably with radio quality and levels. 

I mix the tune in the DAW using the FX and compression I have available. I do not try to over compress. I like to keep some dynamic range in the wave. Upon export, I double check all levels in the tracks and in the busses to be sure nothing it clipping (in the red) . An occasional blink of red is OK in my experience and has never caused me problems.

OK so I export it with 'What you hear" into a folder to receive the new wave. 

I open it in my WAVEPAD wave editor and trim the starting count in and dead space at the end. I click save. Next I apply Normalization to it in Wavepad. Normalizing brings the highest peak in the wave to 0db and everything else is under that level. Unless there are some wild spikes in the wave, this tends to raise the final volume pretty close to radio/standard CD levels.  

If there are big spikes I would have to go back to the DAW and compress those spikes down to get the levels up without incurring digital clipping in the final wavepad conversion. 

http://www.nch.com.au/wavepad/  It's a free mp3  converter and audio editor.

Yeah..... loudness isn't everything, but it does help if you are trying to pitch your music to be up to at least the level of the other music they normally use. 

Low, weak levels indicate someone who doesn't know what they're doing.

Boost 11 is a very hard limiter. I've used it on some projects and it's really easy to screw things up with it. There are better ways to get the same results without the destruction that can be had with B-11 if you're not careful.