True Neutral is at once the rarest and the most common alignment in the multiverse. Neutral characters are either incapable of making moral and ethical decisions or refrain from them actively. "Actively" is the key phrase here. A character that is incapable of moral and ethical decisions would have intelligence and wisdom scores of no higher than 6. Very few player characters qualify on that account, therefore the vast majority of PC Neutrals actively refrain from moral and ethical judgments. Within this context there are two reasons a character may not actively pursue ethical and moral thinking. The first, and most storied in the AD&D tradition, is the druidical "preservation of the balance" mentality. However, this view, for obvious reasons, is uncannily rare.
The second and most common example is the character that simply doesn't care. Neutrals of this type aren't concerned for the welfare of anybody (except themselves), but they aren't willing to advance themselves at any cost like Neutral Evil characters. They are comparatively lazy and lacking in drive in this respect, still there are certainly other reasons. The character may see advancement beyond reasonable comfort through reasonable risk as pointless. Not surprisingly, these Neutrals have a bleak view on life. As for the ethical (law vs. chaos) leanings of these characters, they may follow orders if it serves them, disobey if it doesn't, act on the occasional whim but otherwise keep to a reasonably predictable life.
True Neutrals are all about reason, and perhaps that's why they are so few. Everybody seems to get behind some banner or cause, Neutrals couldn't care less about such trivial matters. Often they have one fascination in their lives which they are preoccupied with, and everything else doesn't matter to them. In the case of druids, this is the "preservation of the balance."
True Neutral societies are very rare, but when they do occur they tend to be primitive. The concerns of simple survival dominate the daily lives of such people, and for them further complications aren't worth the effort to create. In a way, Neutrals are the most peaceful of societies, but they are also the most infuriating because of the nearly universal lack of a drive the members of this alignment possess.