Last year I had to learn a complicated rhythm as part of a breakdown section of a song in my progressive rock band. This part of the song is in 6/8, yet there's a predominant "4 over 6" feel to it.
I came up with this part where I start out playing 4 over 6 on the bass drum for two measures, then adding a left foot hi hat on every down beat for the next two measures, followed by a snare side stick that mirrors the "4 over 6" bass drum, but with two beats instead of one. Then the hardest part, adding a ride bell with my right hand that plays groups of 3 over the whole thing.
My description probably doesn't make much sense, so I gridded it out.
Doing the kick and hi hat together is really easy, then working in the side stick on the snare wasn't too difficult. But once I started playing the ride bell on top of all that, it started falling apart! So I broke it out and worked on every 3-limb combo simultaneously (i.e. kick, hi hat + ride; or hi hat, snare + ride, etc.), before gradually adding that 4th limb.
It took some practice, but it was starting to come together before I finally decided to abandon adding that 4th limb for a slightly different approach, as building up that 4-limb pattern took too long and the song felt like it was stalling out in that spot. So now after adding the 3rd limb, we go right into a heavier part of the song where I play a groove with lots of fills. But it was fun working this up!