Did you discuss salary during the interview?
It’s generally inevitable that you were asked about salary during the interview process. If you were able to defer the topic (see Interviewing, Sample Questions and Answers), you can start negotiations, if any, with a clear slate.
If you agreed upon a range, is the offer at the top or bottom? Most employers like to start new hires below the midpoint for the position. That gives them room to award generous raises to employees who are doing a great job! If you’re right at the bottom, there may be room to move up a bit. If you’re over the midpoint, you may not have much leverage unless you can point to very critical skills in short supply.
If you agreed upon a specific salary or a very narrow range, you have very little room for salary negotiation, unless the offer came in below that amount. You can still negotiate other elements of the offer.