What is the first step in balancing a redox reaction by the half-reaction method?

First step is to balance the amount of atoms on each side

So for example if my equation that I have to balance is : Br2 - > Br-

First thing I would have to do would be:

Br2 - > 2Br-

Then I would have to balance the charges on both sides. So because there is a - 2 charge on the right side I will have to add a - 2 charge onto the right side as well. I would do this by:

Br2 + 2e - - > 2Br-

And now you can see the amount of atoms and the charges are balanced ... So your overall reaction is now balanced too.