This might seem like rather odd advice to give to person- after all it's something that most kids learn at an early age. But for someone who might be autistic, this might not occur to them at all.
I've always been good when it comes to grooming- especially when it comes to taking a bath or brushing my teeth. But I do remember that after I grew a goatee, it took me a while to realize that I had to keep it neat and trim. Walking around with a scraggly goatee probably didn't help me on the job front way back when.
None of this is to say that anyone with autism has a problem with grooming, but is something to know about.