Security is a very very large field. What specific area of security are you interested about getting into?
It seems like you have a lot of experience in the administration world. You can use that as a starting point to get into security. Study up on hardening servers, networks and what have you. I know that Cisco and RedHat have security certifications about hardening their specific products. You can look into that.
If you like development work, learn about how to develop secure applications. Read up on common attacks like XSS, SQL injections and buffer overflows and try to minimize them in the code you write.
If you want to get into the offensive side of things, learn how to exploit the common vulnerabilities. There are many resources available that allows you to practice including hackthissite that allows you to hone your skills in a safe environment. Get familiar with the tools in Kali Linux/BackTrack, there are many useful ones in there. Pick up a scripting language like python or ruby, this will be immensely helpful when you need to automate task or write proof of concept exploits.
Certification wise, CISSP is the industry standard. OSCP is an excellent hands-on certification as well. I heard good things about the various SANS certificates but they are costly. Very costly.