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I need to learn more about frontier orbitals and organic chemistry. Any references?

In electrophile aromatic substitution, how do you know the degree of hardness/softness to the attacking electrophile? And how do you decide the hardness/softness of the aromatic ring based on the already existing substituents?

I have a calculated HOMO and LUMO energies for a group of molecules. But sadly, I dont now how to use it to predict reactivity.

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A great book for this is Frontier Orbitals and Organic Chemical Reactions by Fleming.  He talks all about this kind of stuff.

If you have the HOMO and the LUMO for your two pieces calculated then it should be easy.  Add the higher energy HOMO into the lower energy LUMO.