Jackal : you are really a constructive guy ...
b00ms1ang : First I think they must learn pratical network/systems & dev things, like wireshark
After, like others said, learn them reco/enumeration/scanning and when they understand perfectly what they see learn them how to find vulnerabilities and exploit them.
You have many topics on this forum for this kind of question
After you want to know what I do, and what techniques I use ... in fact it depends on what I'm faced so reco/enum !!!