Toothpick works well for the hinge areas. You can then poke the toothpick into a damp tissue (water or lemon juice) & use its point to work the tissue into the hard to reach areas.
You can then use the same tissue (this is why I prefer lemon juice) to wipe the Airpods themselves & the outside of the case. When they all start to feel grippy again (& lemon scented
), then job done.
But, you've gotto get on top of the areas on the case that squish fine, metallic bits early or else they'll be stamped into the case forever...yet to find a product that wipes them totally clean.
I haven't cleaned the inside where the battery contacts are yet - surprisingly, after over a year, it's still clean in there with maybe one or two specs that I can see....but a cotton bud (DRY!!) should clear them out easily.