Balancing the electron flow in the external circuit (Voltaic Cells)?

When drawing such a cell, I recommend writing out your half-reactions. Determine which element will be oxidized and which will be reduced. You should have a chart with reduction charges that will help you determine this. Of the two charges, flip the one that will make the reaction positive. What is at the anode is oxidized, and what is at the cathode is reduced. The ions move I suspect because it is easier for them to oxidize than to reduce. (Atoms/ions, etc, like to move where their activation energy is lowered)