Sometimes you have to multiply:
Cl2(g) + 2e- 2Cl-(g)
And Al(s) – 3e- Al3+(g)
Note that these are already balanced for charge and change of oxidation states
We have to multiply by 3 before adding to doubled :
2Al(s) - 6e- + 3Cl2(g) + 6e- 2AlCl3(g)
Or 2Al(s) + 3Cl2(g) 2AlCl3(g)
Again, it depends on the question ......