When it's time to ask your boss for a raise or promotion, do you find yourself clamming up and getting nervous? Do you end up with your foot in your mouth, saying the wrong thing (or two) at the wrong time?

What makes it so hard for some of us to effectively negotiate?

Maybe it boils down to lack of confidence, or maybe it boils down to lack of preparedness.

It's important to know ahead of time what to say as you begin negotiations for any deal. Even more critical is knowing what not to say. Avoid these words or phrases and you'll find negotiation success in no time.

"I guess" or "maybe."

If you are not firm in what you are asking or negotiating for, you could leave a lot of money or other benefits on the table. Know what you are after, and lean in.

"I don't know."

Know why you want what you want, because you will be asked for an explanation. Director of career services at Columbia University School of Public Health, Heather Krasna, says it is imperative for you to do your homework ahead of time: "This includes comparing the tasks you handle in your current position and how they relate to similar jobs in your industry." Plus, if you find that you are doing much more than what is included in your job description, you will have leverage during negotiations.

"I'll be honest."

Perhaps saying "I'll be honest" sounds like a good idea. Say this and it will make you sound like you're passing along valuable information about your wants or needs, right? Unfortunately, saying this phrase could easily backfire. It suggests that up until that point of saying this sentence, you haven't been fully honest.

"Or else."

In the professional world, tantrums and ultimatums simply do not work. As career expert Vicki Salemi says, "Your behavior ultimately sets the tone for the meeting." Use a positive tone and language, because any sort of threat will get you nowhere.

Remember: always angle for the salary, raise, and benefits you deserve. Just make sure you watch what you say.