here's a few suggestions to get you some "instant gratification." I don't know your experience with Mesa since you're new to the forum, so I'll just go on for a little bit. Sorry if you already know this stuff...
-Set all the knobs to 12 oclock. Engage the effects loop and put its send and return knobs to 12 also. This engages the Output knob. Put this knob at 12. Then adjust each channel's "Master" volume to a reasonable volume. If you can afford to go loud, 9 oclock is what I would suggest. This will give you some great power tube saturation at a somewhat reasonable volume.
-Most people typically set up channel 2 to Vintage mode to do their leads and solos. Channel 3 is typically only used on Modern mode for pure mayhem :twisted:
-For metal riffing type stuff, on the back of the amp set the switches to Bold and Silicon Diodes. You may also like Rectifier tubes if you like a creamier and warmer sound, but it won't be as tight.
-Once you got this stuff set up, make sure you plug from the 8ohm jack of the amp to the 8ohm jack of the cab. USE A SPEAKER CABLE! DO NOT use a regular guitar cable. The thickest and shortest speaker cable you can find is preferred.
-Be sure to click the bias setting to 6l6, not el34. Unless you have el34 tubes, but all Mesas ship new with 6l6.
-Finally, plug in your guitar, then hit the Power On switch. Wait at least 30-90 seconds, then hit the Stand By switch up. Hit a fat chord, and smile.
On mesas, you will find the knobs are VERY sensitive. It will be worth your time to read over the manual. All the knobs have sweet spots that fluctuate around the center 12 oclock position. Turning one knob affects the others. Think of the knobs in this manner:
Bass=tightness>boom>muddy sound.
Mids=scooped>liquidy/creamy>stiff
Treble=dark>focused attack>shrill
Presence=dark>bright and chimey>shrill
It is often better to cut things out rather than boost everything. So if you want more treble, you may not have to boost the treble, but rather cut some bass out. Cutting bass and boosting mids always gives greater clarity.
Let us know how it goes!