Best tip: read the
iZotope pdf on mastering. Then read it again.
For mastering, use Ozone for your final conversion to 16 bits. Set SONAR's dither option to "None" and enable MBit+ dither in Ozone. Set the brickwall limit at -0.3db and make sure to check the "prevent intersample clipping" option.
Everybody loves the compressor in Ozone, but the paragraphic equalizer is every bit as cool a feature. Set the averaging to Infinite when EQing the entire mix, set it to 5 seconds if using it on a vocal track. Be sure to try both the Analog and Digital modes; one will probably sound better but which one depends on the material. (Analog mode is a little easier on the CPU). Make a reference curve from your favorite commercial CD, but don't use it for EQ-matching, just as a visual reference. Start with the spectrum display in critical-band mode, then switch to normal spectrum for fine-tuning.
The multiband exciter is the next-coolest feature. I use it on drums and vocals primarily, although when used sparingly it can also be applied to the mains. For vocals, set band 3's range from about 1.5KHz to about 4KHz and bring it up until the vocal starts to sound tinny, then back it off. Use just a little of band 4 - too much will emphasize sibilance. For drums, use more band 4, with the crossover set to between 2KHz and 4KHz, to make cymbals sparkle.
Beware that the exciter will change your overall EQ, so you have to go back and forth between the two effects.
The stereo enhancer is a nice subtle effect across the mains. I wouldn't use it on individual tracks. Just use bands 3 and 4. Set the delay on band 3 to +8ms, band 4 at -8ms, just as a starting point. Use more enhancement on band 4 than band 3.
Sorry, this wasn't a very well-organized response. But there are lots of other happy Ozone users here who will gladly share their experiences, too.