My main tip is to be consistent.
Get it right from the start of the lesson: have date and title ready on the board; greet them at the door; point out ties that need doing up, shirts that need tucking in etc as they arrive; make them stand behind their chairs until you let them sit down; stand them back up again if they start talking...
Then follow your school behaviour policy, and if that is unclear then set up your own. I do one verbal warning, name on board for second offence, sent outside for third. At that point, I judge if the child is going to settle if they come back in or if they need to go elsewhere.
Oh, and remember to praise! "Thank you Lauren for sitting in silence", "Eddie's already answered questions one and two. Brilliant", "oh, great idea. I'd not thought of that"