Law versus Chaos: Actions that place the group over the individual or others over self. For example, if a cleric is constantly using his spells to buff the party or other party members, that would move him more into the realm of Law. If he only used his spells to benefit himself, I would move him more towards Chaos. A balance between the two would be Neutral.
As for Good versus Evil, I happen to like the in-depth discussion on it in the Book of Exalted Deeds. Things like helping others, charity, mercy, and forgiveness, particularly at a character's personal expense, would move them more towards Good. Things like slaying non-combatant members of evil monster tribes, torturing a captive to gain information in order to prevent an attack on an innocent village, etc., would be Evil.
So, from your initial post:
Picking pockets: Chaotic act.
Attacking without provocation: Evil act.
Example of a Good act: Healing a beggar.
Lawful act: Turning said beggar in to the Watch for breaking law against panhandling.