Well there is a lot on Youtube & SecurityTube. The Kali Linux forums are helpful.
Learn Linux if you don't already know it. I don't mean the GUI. Learn how to admin stuff using the CLI.
Understand about the daemon processes that serve stuff e.g WWW. Learn about the OSI 7 layer stack.
Get into TCP and IP. Learn Python and start write simple little tools. The Scapy library is a great boon.
Learn about how Wifi actually works and why WEP is a disacter waiting to happen. Security Tube is a fantastic source of info.
The site is owned by Vivek Ramachandran, he worked for Cisco and in the technical development of the wifi systems.
Understand how WPA and WPA-2 work and how you can try and subvert it.
Start playing with the old favourites like the LAND attack and the Teardrop attack from the Win 95/98 days and how they worked.
Google is your friend, look up Google dorking
http://www.hackersforcharity.org/ghdb/
Read up on SQL and how to write queries in SQL to perform SQL injection.
Basically to defeat something you have to understand something.
Knowledge is Power.