[Image above is from https://www.nerdwallet.com/blog/loans/student-loans/negotiating-salary-study/]
First question to ask yourself: do I have a salary requirement?
If not, do some homework. If so, do this homework anyway to see if your number is realistic. 😉
Look on Glassdoor or other. Research salaries of roles in like companies in the same geography. Compare those with a little research on LinkedIn to gauge experience of people in those roles at those companies.
As others have suggested, I would always try to get the company to state their number first. Ask: “What is the salary that you have budgeted for this role?”. If they balk, they’re lying (or not serious about the role or not well organized and that is a red flag altogether). You can get them to provide a number by saying something like: “While numbers matter, it’s more about the work, the culture fit, and the opportunity for me that matters. I’ll weigh all of these factors in my decision”
Also, remember salary isn’t everything. But don’t accept anything far below your number. It is okay to sacrifice a small percentage for other factors (benefits, culture, interesting work, stock, etc.). And if you do, always ask for a 6 month review to re-assess.