How much do you leave for the reader and how much do you explain? Does this depend on genre? It seems to me that "good" writing leaves room for the reader's imagination to fill in the gaps. But sometimes I've read reviews, usually of genre books, that complain that the writer didn't make everything clear. Are these lazy readers who want everything spelled out, or has the writer missed putting in some crucial piece of information that the story hangs on? I think it is often the first. Genre readers are more used to being told everything -- perhaps because of a larger reliance by writers on omniscient POV. Their readers are not as used to working for it. Literary readers have to use their imaginations a lot. Crime writers, I suspect, are good at it too, since they all seem to read looking for clues.
John Marsden doesn't describe his characters from the outside. Readers wear their skin, see the world from their POV. I never miss not having these details -- perhaps because I'm not visual. Nothing is more boring to me than a flat description of what a character looks like/is wearing. Some writers can get away with telling these type of details because they do it with such fresh, arresting details that the reader is engaged. But some... Tell me she had eyes like sapphires, and thick, wiry black hair, and I'll be stifling a yawn. A few years ago I picked up a favourite horse book from my childhood years and was astonished to find the opening sentence was something like "So and so wore fawn jodphurs, a tweed riding jacket and knee-length black leather riding boots, and her horse wore a dressage saddle and an eggbutt snaffle bit". Oh, please.
It's hard deciding how much to explain to a reader: I'm writing fantasy so do I go with a more maximalist effect or make them work. In the end, I usually try to make them work because I do believe it's better writing. More satisfying for the reader who does do the work and puts together the clues.