The two most important features on the FLX-30BB are Frequency and Power. Together they help you to perfect your screen readout in every fishing scenario you can put it through. When adjusting the FLX-30BB I usually start will adjusting the power output between LP (low power), MP (medium power), and HP (high power). Here is my power to depth chart that I use:

LP) 20ft and under
MP) 20-40ft
HP) anything over 40ft

The next will be frequency, I usually like to look at frequency as a fine tuning tool. Each frequency has its own cone angle. The frequency range is from 160kHz - 300kHz, and a cone angle range of roughly 16 Degrees - 7.5 degrees. The higher the frequency, the narrower the cone angle. This is a very useful tool to "dial in" your unit once you have set your power level accordingly. Here are some scenario examples that I have found for unit set up.

1. Shallow barren bottom: Low power, low frequency to see a larger viewing area.
2. Shallow weedy bottom: Low power, high frequency to shoot between the weeds. 
3. Deep water flats: Medium Power to High Power (use depth chart above) Low frequency when searching for the fish and then switching to high frequency when on top of the fish to achieve better sizing of the fish.
4. Steep breaks: Use depth chart for power level, always use a high frequency, this will give you the smallest amount of dead zone.
5. Soft bottom: Manual Depth range, medium power (depending on depth) and a mid-level frequency 200kHz-250kHz

Note:

When using Low Power and Medium Power, the unit must be in a manual depth range. When reducing the signal strength the unit will have a difficult time locking onto bottom in Auto Range. The same is true for the on screen depth readout which is why that is disabled in LP and MP.