Often disdained as the paladin's goody-two-shoes alignment, Lawful Good is a far more subtle alignment than that, for very few characters who happen to be Lawful Good actually stick to anything approaching the Paladin Code in stringency.
A lawful good character holds strongly to the principle that the good of the society can only be maintained via order. The exact specifications of what is "good" may vary wildly for this purpose, but on the whole "good" implies concern for the safety and comforts of others, and that all persons have a right to safety and comfort. The character may build up other definitions in their own moral code, but this is essentially the heart of the matter. Lawful Good, unlike the other Good alignments, also holds that it is sometimes necessary to sacrifice what is "good" for a few persons in order to preserve order, which is "good" for society in general.
On a personal level Lawful Good characters have a tendency to at least strive for an ordered lifestyle. Many, if not most of them, have an "everything has a time and place" attitude. Most tend to organize their behaviors to suit the group, although they are reluctant to do so at a personal loss unless something worthwhile can be obtained with the sacrifice.
A Lawful Good alignment does not rule out chaotic behaviors, particularly impulsiveness. Impatience is another fault that some Lawful Good characters are guilty of. On the other side of the coin, hedonistic behavior is not often observed in Lawful Good characters, unless in one or two activities.
While Lawful Good characters believe that order is the best way, they don't necessarily maintain it. A character with a particularly poor willpower may allow his life to get quite out of shape. And also remember that the character will maintain order from his point of view. A Lawful Good merchant's shop may look like an explosion in a mattress factory, with nobody other than the character able to find anything. But the apparent chaos is deceiving most of the time, ask him where something is and he'll usually be able to find it much faster than appearances would seem to dictate.
Lawful Good societies tend to avoid overdoing laws. The laws of the society are usually well coded, but one individual, or sometimes a council, has the right to overrule the law to achieve something "good" (or at least perceived as such). Lawful Good justices are more concerned with the spirit of the law and the intent of its author in achieving a worthy purpose. If the law does not achieve this most Lawful Good characters will dispose of it, although some more reluctantly than others.