Hello Sr,
It's all about practicing, I know you already have the idea of what I mean by practicing as you have a core knowledge,
I will recommend you to read the curricula for the CCSP firewall test, and perform some labs on real devices of GNS3 ( you can find a bunch of lab examples on the internet)
There is a book that is comming on september ( all about ASA firewalls )
http://www.amazon.com/Cisco-ASA-All---One-Appliance/dp/1587143070/ref=sr_1_3?s=books&ie=UTF8&qid=1365787419&sr=1-3&keywords=asa
You could give it a try,
remember to rate all of the helpful posts
Julio Carvajal
Senior Network Security and Core Specialist
CCIE #42930, 2xCCNP, JNCIP-SEC