Happy Kentucky Derby Eve, everyone! The Kentucky Derby is one of my absolute favorite holidays--any celebration of seersucker, extremely large hats, and what is effectively a bourbon Sno-Cone™ is naturally well-regarded in the Dr Becca household. I'd give you my own mint julep recipe, but it pales in comparison to this longform version from 1937. I guarantee you, it is worth reading in its entirety.
Anyway! I've been wanting to tell you the extremely exciting tale of how negotiating my startup went. And really, the best advice I can give you is this: Know Thyself. The better you can back up your startup list, the more likely you're going to get what you ask for.
Negotiating is most likely going to happen between you and the department chair, which means that you want to have good lines of communication open with this person. Approach negotiations with the attitude that the chair is on your side--it's obviously in the department's best interest that you're successful, but you need to make them confident that the things you're asking for are directly related to your success. To that end, you need good, concrete reasons for why you need/want these things.
This can be especially important in diverse departments, where the chair may not necessarily have a good understanding of the intricacies of your research. This was the case for me, and because I would be bringing several new techniques to the department, I had to be prepared to explain not only how each of these things worked and fit into my research, but into other faculty members' research as well--how they would be an investment for the department as a whole.
In particular, I needed a relatively big, expensive piece of equipment--one that is not usually included in a new hire startup. Let's call it The Beast. I spent a loooooong time discussing The Beast with the chair, and as a result, she went to bat for me, hard core. First she contacted the chair of another semi-related department to see if they'd be interested in going in on The Beast together. He initially expressed interest, and then backpedaled and said that he wanted a Beast of his own for his department. She continued to ask around, branching out to departments you would normally not think of as interacting with hers, and amazingly, she found one.
She did not just find a Beast that I could get a few hours of time on a week or whatever--this Beast is basically brand new, and literally nobody is currently using it. Though it will have to remain in its home department, I negotiated supreme administrative control over its use, complete with a technician to manage the day-to-day Beast bizness (among other activities). And yes, it's all in writing in my startup letter.
Each of us is going to have different needs to do our work successfully, so I don't think taking you through each thing I negotiated will be all that useful (that said, happy to answer any non-pseudonym-destroying questions in the comments here). What I do think helped me the most was the patience to discuss and explain my needs as much as was asked of me, and that I had a clear, communicable vision of what I wanted my lab to be like. In the end, I am extremely happy with the package I got. I can't wait to start spending all that moneeeeeeyyyyyyyy!