Here's an easy rule-of-thumb for modulation... if there's an attenuator or attenuverter (a knob that controls the amount of anything) in the patch, you can insert a VCA into the chain and modulate THAT.
That's not the only way to modulate something. But it's one of the easiest ways to bring some "movement" into your sound. Not all modulations have to be these huge sweeping affairs. Even some subtle amounts of modulation can go a long, long way... especially when you are modulating multiple things.