Every time I bounce my songs there always too quiet and I have to turn up my ipod to hear them.
Once you've bounced your mix down to a single wav file, you need to open it back up and maximise the volume, get the stereo image right and use fine EQ/multiband compression the track so the frequencies are as balanced as possible.

Real mastering demands years of experience and $$$ of top-end gear, but the general idea is just to make sure your track(s) will sound good on any different system.
Burn off a CD of your mix and try it in a car stereo, through PC speakers, through a good hi-fi, whatever's available. If you start to notice it sounds bassy/tinny through several of the systems you can tweak the eq slightly when mastering to compensate.

Upstereo is a great, simple freeware plugin which boosts the volume and stereo spread to give more of a pro sheen to your recordings. Give it a try.