1) Make a list of what is most important to you: Is it the reputation of the university, the quality of the students, the cultural environment, the outdoors? Those things you cannot really negotiate, but they may drive your decision. Or is it research support, salary, title, teaching load, etc? All of these things you can negotiate. If you want to bring these up, prioritize. Don't just list everything, simply because you have heard that other people have negotiated these aspects of their position.
2) Be positive, be open, and be straightforward. People get annoyed with you if they think you are wasting their time, or if they think your just a habitually disgruntled academic. When you ask for X explain how this will improve your productivity, and help the department/college/university succeed.
3) It's totally o.k. to talk salary, but try to be informed. What is the salary structure in your current/new department (this is public information in public universities, and not exactly a secret in private institutions)? Where do you reasonably fit in, in terms of age/accomplishment/etc? Ask for a little more than your looking for, but not something ridiculous.
4) If there is an issue that dominates all others, say so (standard example: spousal hires). But if you do make one issue central, you have to be prepared to walk away. And again, be positive ("I love this place, but if university X makes an offer to my spouse, I will take the job.")