Identifying spontaneous redox reactions
For starting purposes, you should write the half cells, either with their oxidation/reduction potentials.
Now if you want to compare the oxidizing species then you have to consider the oxidizing potentials of all the species and the one with highest value will be the spontaneous half cell and the reverse of the other one will occur. 
Remember you should consider only one type of potential at a time(i.e. either oxidation or reduction) for comparison.