How would you balance: Al + Fe2O3 → Al2O3 + Fe?
One must first balance the metals before balancing non-metals such as Oxygen and Hydrogen (Hydrogen isn't involved in this case).
So therefore on the right hand side you see 2 Aluminium atoms and thus one must add a 2 before the Aluminium on the left hand side.
Secondly the Iron must be balanced, on the left it can be seen that there are 2 Iron atoms in
Lastly the Oxygens must be balanced but in this case they already are at 3 on each side and thus the whole equation is now balanced.
Hope I helped :)