I am a student but have done a lot of research into this area. You can get your SANE right out of school and/or take the forensic class somewhere...although there are only a few schools that have a program, Kaplan has a class you can take...expensive though.
As for where to work...I would suggest emergency medicine or ICU. If you can find it, a job at the police or DA's office may work as well. You can also get into death investigation at the coroners office sometimes.
Hold a current, full, and unrestricted license as a registered nurse (RN) in the United States
Have successfully completed an adult/adolescent SANE education program that includes either: (a) a minimum of 40 continuing-education contact hours of didactic (classroom) instruction, or (b) three semester hours (or the equivalent) of academic credit in an accredited school of nursing or other accredited educational institutions
Have had supervised clinical practice until determined competent in SANE practice. Current SANE competency in the care of adults and adolescents must be validated by an appropriate clinical authority.
Have a minimum of 2 years of practice as a registered nurse in the USA or as a first-level general nurse in the country of licensure.
My personal opinion is a minimum of 2-5 years RN experience before becoming certified as SANE.
One can enter into Forensic Nursing right after graduation. There are many programs available. See the sticky thread (at the top of this forum) about different programs for both the Forensic Nurse and the SANE.
I advise one to seek a position in the ED to get the best experience in Forensics. One can also work in the Critical Care Units (ICU, MICU, etc.) to get a good idea of how forensics is applied in those areas.