the way i think of it is the more positive a reduction potential, the more likely it is to happen. if the reduction potential going from Cu(s)----->Cu2+ + 2e- is positive, this indicates that Cu metal IS willing to give those electrons out and become a reducing agent. if the reduction potential of Cu was negative, then the above reaction is not likely to happen, and the reverse will happen making Cu an oxidizing agent.
I'm sure you know all this, but think about it, metals are usually reducing agents so they will usually have positive potentials when giving up electrons. metallic ions are weak oxidizing agents, meaning the reverse will be negative, meaning it will TAKE energy to reduce a Copper ion.