A well planned lesson is always a good starting point - keep them busy and they will be less likely to mess around.
Positive discipline is far more effective, generally, then telling-off - ie picking on good behaviour in the hope that all students (and most do) want to be given positive attention.
Giving "choices" - eg - "James, you can choose to focus on your work, or choose to continue as you are. However, if you choose to continue, then there will be consequences" etc.
A consistent approach is always the most effective, so ensure you know what the school's policy is (is this a teaching interview or a PGCE/GTP type thing? - if it's the latter, then talk about finding out what the school's policy is and sticking with it. If it's a teaching interview (or similar) get hold of the school's policy beforehand - most places have it on their website)
And, as my Dad told me, when I did my PGCE (he was also a teacher) - never threated anything you can't carry through. So (this was Dad's example) if you tell a kid you're going to throw him out of the window, you have to.