I'm current running 13th Age, and there are two players who are quite tactical. The issue is both of them thinks differently and one is pushy, and the other is stubborn. Every now and then the both of them will bicker about their tactics. Sometimes it gets rather heated where both side argued their case (or worse, the plan didn't work out and they resort to "I told you so.") and I'll have to step in and ask them to chill.
However, prevention is better than cure. What steps can I take to explain that I don't wish to see this type of behaviour at the table and what should I do if it happens again? I'm not looking for anything antagonist or personal. I have been GMing for the group for about 6 or 7 sessions but I am not their personal friends, so no ruffled feathers to be worried about - but I can't use our friendship as an Aspect.