Welcome to the forum Spitfire.
Look at your routing within Sonar. Create a master buss to route all your tracks and sub buses to. Bring down all the faders on all the track and start mixing from there. Watch the levels in the master buss you created. Don't let its level go above -3dB peak.
Avoid letting a track become too loud on its own. Whatever you do avoid allowing any track or buss to getting into clipping even though Sonar wont distort if you do.
Use a limiter on the master buss to avoid peaks that go to clipping. But its best to use that for insurances only keep the overall mix below -3 dB. Many like to keep it at around -12 dB.
You can have as many buses as you want for all sorts of reasons. One reasons is to group like instruments together.
There is a lot to know about mixing but this very short post will get you started.