It is sad that not everyone will have the privilege to negotiate salary because of how bad they need the job or the nature of the job.
The best way to negotiate is by sharing your experiences, how you've helped former firms (you actually have) and your skills.
Thanks for your comment! Honestly, many people can't negotiate salary because of job requirements. However, highlighting experience, skills, and previous contributions creates an opportunity for negotiation. If salary isn't possible, at least other benefits can be discussed, which could be beneficial for your future career.