Rule #1a - never be the one to throw out the first number. Make them do it and negotiate from there.
Rule #1b - never discuss your salary history.
Rule #1c - know the going market rate for your position.
Rule #1d - remember to think in terms of the full compensation package and not just salary.
If they bring up salary again and want you to throw out a number, first try to steer the conversation back to what you will bring to the organization and that you're certain a fair salary can be agreed to once you've both agreed to a mutual fit. If they still press you for a salary, then I'd recommend going in with a range at the higher end of what you're looking to get. That will give you a little room to "give in" and negotiate down and still get what you want.