To me the hardest thing seems to be to get my two hands working independently yet together. Most patterns I come up with fall into the modal-stay-the-same category. Meaning you put the fingers on the right notes and nothing really changes. This example switches between two tonalities and on top of it runs a four-note pattern in the treble against a three note pattern in the bass.
Every three measures everything lines up.
The first three measures produce a B minor melodic sound. The last three measures are harder to define as the bass notes clearly line out an A minor triad and on top is something like an A major augmented #11.