There are many reasons to negotiate salary. Future earnings are generally a percentage of your current salary, so your lifetime earnings will be significantly higher when you negotiate. Also, most employers expect the applicants to negotiate.
Research what the market pay is for your industry area. There may be differences based on experience level, cost of living in the city, company/organization size and type.
The best time to negotiation salary is after you receive a job offer. This allows you to know what the employer is willing to pay so you don’t price yourself too low.