Welcome to the club. There is no short answer. Slamming your mix with a brickwall limiter will (short term) "make it seem" louder (and it will indeed be a bit louder), but there is SO much more to it. Subtractive EQ is your friend. Find out which frequencies (on which tracks or busses) are "pushing" the mud factor. (Hint: it often isn't the ones that "seem apparently" the loudest.) Do lots of cutting in the 350 htz range. Get your mix to be in the ~ -15 RMS range WITHOUT any master buss limiting first. THEN (and only then), try something like Ozone 5. And be gentle. What seems like "ear candy" at first listen will become headache-inducing at repeated listenings. Get the mix to be UNBELIEVABLY good first. Only then play with limiters (gently). It will take time, but you will get there. Have fun! : )

Meter !! Sonar can show both peak and rms in the meter, and it is quite accurate
when compared in wavelab's metering.

When mixing, descriptions in post's above is good 
 
Dont go hotter than -9db RMS, you want some dynamic's !! People got  a Volume control on they'r stereo for a reason ;D

If rms is less, as an example : RMS -6db to peak, sound will sound distorted ( in my term, i call it RMS distortion ! )

There's 2 kind's of distortion: peak distortion, and the rms distortion, good luck mixing :)

How to set Meter's to peak+rms in Sonar , just right click in the inspector's meter: http://img209.imageshack....9/2842/sonarmeters.jpg

Need a good Meter/Limiter, get the Fabfilter limiter, it got loads of metering.

 http://www.fabfilter.com/...ckwall-limiter-plug-in