Many of us are employed, and while we might have a salary review each year, we often don't get to negotiate much about the amount. We might periodically ask for a raise of some sort, but what should we ask for? Most of us have accepted employment at some point, responding to the offer of a job. Do we know what a fair salary is for our position, in our location, with our experience?
Human Resources and Personnel departments use surveys and information to set ranges of pay for different positions. They come to a salary negotiation with some idea of the market, which is a generalization of what an employee is worth. This could be quite different than what you specifically feel you should be paid. However, do you have any rationale for your demands?
Every year Brent Ozar runs a salary survey. He gets lots of responses and does a better job of this than most other places I've seen. Including me. I've done this a few times, but I'd rather just let Brent run this and view his data. This year he asks you to look at the list of questions and give feedback.
I think Brent has a good list of questions, but perhaps there is something you wish you'd have known before you last negotiated salary. Is there something that might help you decide if an offer (or raise) is fair? Perhaps you want to add a checklist of responsibilities (BI, DBA, dev, etc.).
Maybe you think it would be interesting to know if there is on call work, or even the number of hours your employer expects you to work? Given the pandemic I might ask if the company is allowing remote work or expecting people to come back to an office. Some people have suggested these in the comments, but read Brent's answers. He's looking for a indicators or features that affect salary, not necessarily how you feel about the environment. I added one about non-monetary compensation like training, but feel free to comment on other suggestions as well.
What's really important here is that you take the survey when it comes out. Even if you don't like the questions, getting this data compiled for our industry helps us all, so keep an eye out for the survey and fill it out to the best of your ability. Then get the results when they are published and use them to try and evaluate if you're being compensated fairly.