The best way I have found to 'tweak' a detector is to start with the factory-suggested settings in the instructions. Many on this forum have suggested making a test garden with various coins, gold and silver targets, nails, bottle caps, pull tabs, etc. You might try this over different types of ground in your area as well.
Go over each target a few times until you get the feel of what the detector is telling you with the settings you have. Then work with one knob at a time, going from low to high extremes gradually, re-testing each target at each increment. Depending on how many knobs you have, this can take several hours or days of detecting time, but you will learn what each knob does and where the best setting is.