Its tricky. And, to be 100% honest, it is compounded by the fact that people who game may not always be the best communicators (at least when there not in charecter).
Take the lead: Do you see something you think is problem, try to bring that up, preferably in a billateral situation. That quite guy that never complains may feel the same.
Read in between the lines: Sometimes a comment or dispute on a game detail is just that. But, a player may note how something is bothering them sort of obliquely. Or, at the other extreme, sometimes people seem to get hung up on very particular things, to the point they look crazy. And maybe they are (they really want to be a ninja). Or it reflects something that actually matters, like dificulty in playing the charecter, the charecters relative power/opportunites, game pacing, and so on. But for some reason they aren't saying it like that. They are saying how their ninja should be able to teleport.
Who gets the grease: Overally aggresive, overbearing, passive aggresive, munchkiny, anal, in play, out of play,...it might be subtle, it might be like an actual orc at the table, but watch out here. I don't say "don't play favorites" for any reason of fairness or philosophy, but just based on hard experience. Be sure not to have things revolve around the one guy who actualy vocalizes. (This also applies to the dynamic between the players. Step in as a last resort, but do so if needed. And don't make it worse.)
Don't sweat it too much: and with all that, if they keep coming back, maybe the best way to be a better DM is to run a game you like, and learn from the mistakes you know you are making.