Have you studied about the activity series. That is a list of metals that shows the reactivity from top to bottom. The most reactive metals are at the top and the least reactive are at the bottom. Here is the important part. Any metal will displace the ion of another metal BELOW it (but will not displace the ion of another metal ABOVE it). So here is what you do.
Place iron wire or bar in CuSO4 solution and see if Cu plates out. It will.
Fe(s) + CuSO4(aq) ==> Cu(s) + FeSO4(aq)
Place Cu in FeSO4 and see if Fe will plate out. It won't.
Cu + FeSO4 ==> No reaction.
This shows that Fe is more active than Cu because Fe will displace Cu(II) ion from its compounds but Cu will not displace Fe(II) from its compounds.