1.Don't bring up your co-worker's salary. First of all, you may not have all your facts right, and bringing up your colleague's salary will put your manager into an uncomfortable position. What you should do is compare what you're making to the industry average. Using the industry average will reflect well on you and will show your boss that you've been doing your research.
2.Don't make it personal. The reason for your raise will be professional, so keep that in mind when you're asking for more. What you need to do is write a list of your wins at work, which will show your boss that you do deserve that increase in salary.
3.Don't get emotional.If things are not going your way or if you feel that your employer is wronging you, don't get emotional. Collect yourself and don't let your boss see that you're upset. Instead, take some time to think it over after your meeting to carefully craft your next move.
4.Don't respond immediately if you're unsure. If your boss offers you an alternative and not the raise you're asking for, and if you have some doubt about it, don't immediately agree to it. Instead, ask her if you can take some time to think about it and let her know that you'll get back to her about her offer soon.
5.Don't be inflexible.If your company doesn't have the resources or the budget to give you the raise you want right now, there can be other arrangements you can make with your boss in the meantime. Perhaps more paid time off days or the opportunity to work from home — find out what your manager is willing to give you in lieu of a raise.
6.Don't give ultimatums.People don't respond to threats very well and your manager will not be very happy if you give her an ultimatum. If you have other job opportunities, don't wave them in her face — just gracefully move on if you have better chance of advancing elsewhere.