This is the most open ended question considering the parameters that the expression pedal can manipulate. I would just start with the presets and see how the different value changes affect the sound. The quick reference guide shows what the expression pedal is changing.
Actually, rather than using the bypass switches to turn effects on and off, I have the expression pedal set to change the mix from zero up (in addition to other settings as well). Then, I can blend in delays appropriately for the situation. Lately, I've only been using a couple of presets instead of a bunch where I had created delays with different "intensity". The other advantage is that it's another "on/off" switch using in this manner.