When manipulating a digital synth, find a parameter or macro that dramatically changes the overall sound with higher or lower values. Then, take an external LFO that and play with its settings. Link that LFO to the interesting macros or parameters of the synth and you'll either end up with a giant mess of sound or perhaps you've found the next main element in your track. Either way, keep playing with the synth and LFO parameters until you get a satisfactory result. If you think it doesn't sound good no matter what parameters you're tweaking, then try using a different preset for both the synth and the LFO.