It depends what you've done! If it's something simple like being irritable, wait until the dust has settled, make sure you can make eye contact, and apologise sincerely, then drop it. Ensure you don't use the word "sorry" as a glib get-out-of-trouble phrase, which means it loses its meaning, and is useless when you really need it. Sincerity is the key, chocs and flowers are optional.