I was on a CGM that has since quit selling in the US market - I've worn the MM and Dex - for me the Dex has been a little easier - but with the MM - here's my top few things that gave me the best results:
1. Wait to calibrate until you've got a stable window with your blood sugar (not mid-spike or drop) if possible
2. Try to calibrate while your blood sugar is in your target range
3. Keep in mind that these devices all come with their own learning curve - you can get it to be a useful tool and it may take some playing around
Also, there is a diabetescgms group in Yahoo groups with a lot of good information.
Best of luck and keep us posted on your journey down this new road!