Look at the exam topics online
Read the Official Cert Guide (OCG)
Use the Boson NetSim questions for this test
Re-read the exam topics online
Look at any cisco whitepapers about topics you still don't understand
Cisco whitepapers are just things hosted on cisco.com. A cursory google search will find most everything if you know what keywords to use.
try to get INE's CCNA Security's video material, and if you can through your college get assigned into the Netacad course, its very useful.
Avoid relying on official cert guide, it was horrible for the exam, not enough info, and doesnt even cover the all of the exam objectives.
try to get access to Cisco ASA and practice on it, knowing it is very useful and knowing the modes ASA run in.
go over the exam objectives one last time, and see how well you know those subjects.
I'm sorry to hear about your experience with the exam. A lot of us here have had very similar experiences. It sounds like you have a good overview from the Netacad course but were under prepared for the advanced topics, which are nearly half of the exam. I would strongly suggest the Boson NetSim questions for filling this gap in your knowledge. The explanations for the answers they provide, and more importantly the links to more information, are invaluable for these advanced topics such as FirePower, ISE, etc. Additionally you may want to get a lot of lab work in on the ASAs with aaa and vpn stuff. After my similar experience I followed someones advice on the Boson questions and was successfull in my second attempt at the exam. I hope this helps, good luck!
Get the digital edition of the 31 Days Before book:
Boson Ex-Sim Max for practice tests:
If you had NetAcad then you should already be comfortable in ASDM. As Kyle says, use the Internet to do deep dives on any topic you're unsure on.
arteq, can you elaborate on VIRL? You may want to describe the hardware requirements, course material written for INE and CCNA Security, etc.
Marcelo, I have no used VIRL but it sounds promising. You will need a minimum of 4 processing cores and >10GB of dedicated RAM, 16GB would be my recommendation. Have a look at the following links for more information:
INE has some courseware for the CCNA Security working in VIRL. Might be an interesting choice: