What Liza said. Well said.

But I think the OP was asking about hand signals - it's pretty much implicit in "looking/thinking ahead," but to be explicit, yes. Keep feathering the rear brake while you signal with your left hand (also signal audibly if you're with other cyclists), then brake, then signal again if there's traffic behind you that might not have seen your signal and/or isn't noticeably slowing, then stop.