Summarize this article:

Use a cotton swab or cotton ball to clean the charging ports—where your AirPods sleep when they’re not in your ears—and other nooks and crannies. You want to remove as much dust and lint as possible from the contacts to ensure that the case continues to charge quickly and to prevent shorting out. Keeping these grooves clean will keep your case looking new. Dampen your swab with a little water or alcohol, as necessary. But don’t use enough to soak the cotton, as you do not want drips falling into the electronics of the case. You can gently work wax and dust from these difficult areas with a swab that is only lightly dampened. This is where bacteria can really get a foothold. A plastic or wooden toothpick should really help you to clean out the cracks and fissures in the case, especially around the lid. Be gentle and methodical, though. Patiently work the waxy buildup free gradually without applying too much force. Here are a few other useful tools that will help you keep your AirPods case hygienic, and looking and charging like new:  Tape or 'tack. Use either one to pull dirt, lint, and wax buildup free; if you’re using tape, use a good-quality product that will not leave behind adhesive. Press the piece of tape or lump of tack firmly into grooves to pull wax and general buildup from the cracks on the lid and top of the case. A soft eraser. Use it to rub stubborn stains and dirt away. A soft toothbrush. Only use soft or extra-soft, and put it to work gently scrubbing dirt, dust, and lint from crevices and the Lightning connector.

Summary:
Get inside the charging ports as well as you can. Get into the grooves on the top of the case. Use a toothpick to work on more stubborn grime.