Answer: What is the underlying 
assumption in the first question that will undermine your ability to negotiate effectively? Here it is, “when you are at the point when the job is being offered to you.”
Negotiating is not a last-minute surprise where you have just days to think about terms. The key is anticipating and planning ahead. If you are to lay the groundwork for an offer you wish to accept, you must start early in the discussion about the job, and that is not hard to do these days. Interviews seem to drag on for months. This question indicates the candidate is assuming the hiring organization asks all the questions, has full control of the process and sets the agenda and timetable. Those are incorrect assumptions and will leave the candidate with very little room to negotiate terms.
One of the principles of negotiating effectively, is to influence the course of the interviewing process by asking reasonable questions and providing reasonable information about your situation in anticipation of the various steps necessary in the hiring process. For example, if you decide after the first in-person interview that you are very interested in the position, send a detailed email and thank you note about the job as you understand it. Begin to control the timetable for follow-up actions. Also, ask how many rounds of interviews are involved and when they will be ready to begin the next round. Explain that you are planning ahead “to be available” to meet their schedule.
Stay in constant touch and find reasons to provide information about your plans and when you can continue with interviews. If you are receiving a pay raise while interviewing, say that early in the process to set expectations about what terms you will want to consider. Update any compensation information you have already provided. You may be out of their range and here is where you can ask what the salary range is for the position. If there is insufficient compensation, there is no need to waste your time and theirs.
Provide a detailed picture of your total compensation when you know you are a possible finalist and you are very seriously interested in the position. NEVER provide just salary information. It is misleading and will set unrealistic expectations about what you will need to be paid to accept a new job.
Ask about benefits offered –or you can outline your current benefits so they know what they must match. If they provide a salary range, with the new laws about not asking for salary, you can say you are looking for a reasonable increase and indicate the range you are seeking. Hopefully there is a fit. (Most companies will look for the lowest acceptable figure in the range when extending an offer.)
At the time you are being offered the position, hopefully, the actual offer should be a reasonable amount that fits what you indicated you are looking for. If the offer is incomplete in that you do not know if the benefits program is adequate or there are questions to be resolved, for example, amount of vacation time, health care for the family, etc. I would very quickly ask to review the benefits material and then put your remaining questions in writing and ask for a meeting with an HR representative.
The representative could explain, for example, company stock awards. This might include the opportunity to buy co. stock at a discount, bonus potential, eligibility for salary review, specific information about your grade level and where you fit within the grade (to know if you are low, for example, and have room to grow or if you are high so you will have less room to negotiate a raise.)
Move as quickly as you can to review the information and let the hiring manager know what your timetable is to be ready to give an answer. Or, you could ask when an answer is expected. Reassure the hiring organization that you are very interested in the offer, so they will not worry that you will turn them down—if that is the case.
On the other hand, if you are very concerned that the offer is not what you want, and there is a significant gap, you need to let them know that you are ready to turn them down to see if that is the best they can do. If they are locked into a lower salary range and have no flexibility, it indicates problems on several levels and I would be very reluctant to accept an offer.