I would suggest getting a college degree (B.S.) in forensic science or some other science-related field. I would also suggest internships if you can obtain one. Perhaps even a job at a police department to start with.
The field is highly competitive now, I'd suggest you just apply, apply, and apply to jobs. Sometimes it is just luck of the draw...I wish I could be more help.
Also, there are over 250 jobs listed in the employment opportunity page of the Crime Scene Investigator Network. Many are entry level jobs. Look through the job announcements to see what employers require. You will find that many jobs require a degree, but some do not. Of course, you will be more completive if you have a degree.