What should a good apology contain?

I just had to apologize to a friend who felt she was left out when group plans were made. It started me thinking about how I am trying to learn to apologize and what I find wrong with so many public apologies of the “mistakes were made” and “if I hurt you…” kind.

I think it is really important not to defend your actions but to acknowledge the other person’s feelings and give a sincere apology without self-justification unless asked for.

What do you think makes apologies acceptable?