Jackal : you are really a constructive guy ...
![Sad :(](http://ez.feedthetrolls.net/Smileys/default/sad.gif)
b00ms1ang : First I think they must learn pratical network/systems & dev things, like wireshark
![Smiley :)](http://ez.feedthetrolls.net/Smileys/default/smiley.gif)
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
![Wink ;)](http://ez.feedthetrolls.net/Smileys/default/wink.gif)
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 !!!
![Smiley :)](http://ez.feedthetrolls.net/Smileys/default/smiley.gif)