Find a "clean" spot of ground with no signals (scan in the all metal pin point mode). Next, hold your coil in the air, pull the trigger to place the machine into the all metal pin point mode (this has a fast retune speed), and while still holding the trigger adjust the Threshold so you can hear a slight audio signal. It may be a bit choppy or broken, but thats OK. After doing this, lower your coil to the ground (in the clean spot) and listen to what the audio does. It will either decrease (go quiet), stay the same, or have an increase in volumn. To Ground Balance your Tejon, you will want to have a slight increase in volume as you lower the coil to the ground. This will be balancing your machine "slighty positive", which is the best way to tune the Tejon. The way you adjust this is with the Ground Adjust knob. Think of this knob as "volume" knob, in other words, if your machine goes silent when lowering the coil to the ground, turn the Ground Adjust knob "up" or clockwise; if it gets louder as you lower the coil then turn the knob "down", or counter clockwise. Keep bobbing the coil while you adjust this setting and listen to the results, gradually working your way to an ever-so-slight increase in audio as the coil approaches the ground.
Once you have it GB'd, make a mental note of where the "pointer" is on the GB knob. It is easy to bump this knob while hunting. The key to great depth on the Tejon is to be sure you are always ground balanced properly so keep an eye on the knob and if it has been moved, redo your GB opperation. With practice, you can do this easily in just a few seconds.
One other thing you need to hear the subtle audio characterstics of iron targets is good high-end headphones. The Tejon has a language but without good headphones you will not hear it. Iron targets have a real "snap" to them, a sharpmess of audio, whereas good targets have a much smoother "beep" pattern. Some big iron will fool me once in a while, but you should be able to get to the point where you can "call" an iron target before you dig it. When you have achieved that status, you can then stop digging those targets based on the signal alone.