If you are bouncing to a final mixdown, then normalising will make them louder, though not the loudest they will go. This is done with compression (normal and/or multiband) or limiting. Plenty of good info on this if you search around here. Beware making it too loud though, overcompressed tracks may sound good and loud initially but can get waering on the ears.
BTW, in some cases I think if you are bouncing to mp3, it may be best to leave a little headroom, e.g. 1 dB. For uncompressed audio e.g wav, aif etc.) no headroom required.