My standard reply is that loudness starts with the first track. If your mix is already pretty close to what you want, then adding a Maximizer or Ozone is all you need. But if not, I wouldn't count on a Maximizer to get more than 3-6 dB more overall loudness at most and what do you do if your track still isn't loud enough?
So my suggestion is to start at the ground floor: choose loud samples, choose loud patches, etc. Be aware of your frequency ranges - don't stack a bunch of tracks in the same range and expect to hear them all clearly. Make choices with your sounds and arrangements that don't have to be 'fixed' in the mix with EQ etc when possible.
Use small amounts of compression across multiple tracks (the "SSL" way), use a little more on a sub-mix/bus when possible, use a little more on the Master Compressor if you can - no more than 2-3 dB reduction at each stage will add up to a much louder mix that doesn't sound like it's being squashed to death in mastering. Make sense? :-)
Giles Reaves, aka 'selig'
Audio Illusionist, Musical Technologist
Selig Audio, LLC