I won't try to offer advice, but here's an anecdote of how not to do it:

In the 90s I applied to the startup where Peter Norvig was chief scientist, to work with him putting his prototype code into production. They decided to make an offer, but first asked about previous salary. I was reluctant, the manager said something reassuring, and finally I just told him. Context: I was a high-school dropout who'd just been working at NASA JPL, where the conjunction of government pay grades and my lack of degree meant a salary you'd laugh at nowadays. Further, I had no real experience with negotiation to help recover from this terrible mistake. So we never got anywhere acceptable from that anchor, and I had to go on to join a different and probably much less educational startup.