There are a variety of guidelines and (ewww) "Best Practices" guides. Be wary of using vendor based guides. The Secret Service has a method, there is always ACPO, and a variety of other guides. It would be very hard without knowing your industry and need to make a suggestion on waht would work best for you.
I believe that if you want to get in to this field you first need to invest in some classes that will help you do this. Remember if you go in because you did not know something that will be no excuse for the mishandling of evidence and then you will never work in the industry again. Be safe and get educated. the education will also help you get the gigs.
Eric Lakes – Certified Computer Examiner, [Edited: No ad links in posts please]
Additionally, search the web for Incident Response and Incident Handling procedures first. Most cases have there origins in IR. That is unless you are working with/for LE or counsel. Plus, always check with local counsel (corporate/company) first. Some IT managers like to jump into the pot without checking the water first -- "It's my network and computer's blah, blah, blah...".
An improperly performed investigation can destroy all the evidence. For example, a linux administrator thinks the system was infected by an unauthorized program. So he search's the complete system for an exe file = find / -name "*.exe" -print. This single command changes the access timestamp on every file in the system and it will not provide any useful information. This did not destroy all your evidence but you will have a hard time trying to identify when the program was used.