Don't shoot yourself in the foot when it comes to negotiating salary with an employer. The wrong attitude or approach will cost you dearly. Follow this advice on avoiding the most common negotiation flaws.
Don't share your "opinions". First of all (sorry to say), they don't care. All you should give them are "facts" of what your total compensation is broken down to base and bonuses or other financial incentives. Keep what you think you're worth out of it. In almost all instances, when a candidate expresses their personal opinion of what they should get, it will come across as presumptious. It could also hurt your credibility if the number you throw out is way off what they were thinking.
Don't throw a number out. If you give them an actual number of what you want to make, you will inevitably either over or under price yourself against what the manager may be thinking. This has negative implications since you will either decrease your offer or not get an offer at all because they think they can't afford you. Just simply give them your current comp and boomerang the question back. Try this ..."Well, I'm currently at a 95K base with a 10 % bonus. As far as my expectations go, I'm open and interested in the best offer you could make me. What do you think I might be worth to your company?"
Don't game the numbers. Don’t ever misrepresent your salary! The vast majority of companies will do minimal to extensive background checks to verify this. So be exact about your base and how your total compensation breaks down. Don’t calculate the net worth of all those things and add it into your demands for your next base salary. Also, don't ascribe a dollar value to your vacation time or medical benefits and use that as a bargaining chip to increase the base salary you want. Although this may seem fair game to do, it is typically a turn off to the employer and comes off as a bit manipulative.
Don't pull a "Jerry Maguire". You know..."Show me the money!". As you tell them you're looking for the most competitive offer, always stress that what counts most to you is the opportunity. Let them know that you understand the value of the big picture. Having a less money-oriented perspective will make employers feel secure that they aren’t hiring someone who can be “bought” (and vulnerable to being headhunted out of their department 5 months from now for a higher offer!).
Don't enable a bidding war. Some companies want that one number that will close you down. Until you’re at the actual offer stage though, how can you possibly give them this (especially if you have an active search)? Ex: You tell them that you would entertain 80K and get another offer two days later at 85K. That previous statement is no longer true now. Tell employers that push you for this that it would be very difficult to provide this magic number because of the variables of your other interviews.
Make sure they have your facts and tell them you are open and that all you would ask is that they simply do their best and make you one offer that they feel is their best offer. If every company just made their BEST offer the first time, we wouldn’t see so many “bidding wars” (which are headache for everyone).