Be a role model. Your authority will be lost if you're castigating someone for poor timekeeping but rolling in to meetings 20 minutes late yourself.
Get to the truth. Get everyone's version of events before taking further action. Persistent lateness may be due to family circumstances; could reports of harassment be a malicious rumour? Have a quiet word first.
Don't knock 'em down. A talking-to should get people back on track, not resentfully nursing a thick ear as though they've been naughty. Show them clearly the effect of their behaviour.
Do it promptly. Quash problems before they develop. Explain what improvements need to be made and over what period. Apply the same standards across the board. You can't let one bully off but punish another.
Go through the right channels. Treat the official course as a last resort. Give people advance warning of any hearing, a written explanation of disciplinary action taken, and make sure they understand the outcome.
Let them go. Persistent troublemaking may show someone doesn't belong in the job. Would both sides benefit if they took their expertise elsewhere? Find out how they got into that position, and don't let it happen again.