personally I find self teaching quantum-chem pretty difficult, but I think if you want to use those, you should also understand the theory behind it.
That being said, I can recommend a few books:
Modern quantum chemistry : introduction to advanced electronic structure theory / Attila Szabo, Neil S. Ostlund
Introduction to computational chemistry / Frank Jensen
You don't need to know everything in there, maybe some rough guidelines what you should understand:
What is a Slater-Determinant and why do we need it?
How to derive the canonical Hartree-Fock equations?
What is DFT, DFT functionals and the Jacobs Ladder of DFT.
If you can answer those, you can have a closer look at some other topics like:
Post HF-Methods (MP2,CI)
Coupled Cluster Methods (better explained here: Olsen: Molecular Electronic-Structure Theory)