"Before you speak, ask yourself if what you are saying is true, polite, necessary, and helpful. "If the answer is 'no', you might as well not say it." - Bernard Meltzer.
1. I can not.
"Whether you think you can do it or not, you are right," is one of Henry Ford's most famous quotes. Some things are indisputable - for example, you can not challenge gravity. But for some other cases, it is better not to use "I can not". Most of the time, what you may or may not do is a choice. Instead of "I can not", say "choose not to ...".
2. A lot.
Sometimes, "too much" can make a sentence seem lazy. Basically, it can happen to say nothing. Instead of "tired", use "exhausted".
3. This is not my job.
If "this is not my job" implies that you are less qualified for a particular task, you may need to rethink what you say. Keep in mind that when you are asked to do something, you need to be open to dealing with work outside of your field because more responsibility means more opportunities.
4. I do not have time.
Telling a co-worker, boss or client that you do not have time is rude. It may also indicate that you have problems with time management. Instead, say, "Can we discuss this when I finish the project I am working on?" or "I'm busy today, but tell me when you need me to tell you if I can take it."
5. You will have it soon.
"Soon" leaves room for interpretation. Without set deadlines, things get lost. Setting a clear date can help you be more responsible. If you need time, you can say "you will have it ready by Wednesday maximum".
6. I do not know.
There is a difference between "I do not know when the shipment will come" and "the shipment was scheduled to arrive on Monday; "I will contact the company and let you know."
Of course not all words and phrases leave the wrong impression, but depending on the context, they can have a negative impact. Knowing what to say in a given situation will help.
Burimet: Inc Magazine, Ladder