Be careful with need: it can show dependency and desperateness. Rephrase stating what you need help with:  

• So I can complete this project on time, I estimate a couple of extra people for two weeks is sufficient.  
• We need to run tests on these samples to establish if they are genuine.  

With the right tone, need can be assertive by showing what is essential.

Be careful with suppose: it can show indecision, indifference or that you do not care. If you are not sure, say so and what you can do to solve the issue:  

• This internet connect is unsecure so we shouldn’t send any sensitive data.   
  
• As we don't know if the internet connect is secure, we shouldn't send any sensitive data.
  
• Although there is much to do, everything will be ready for the meeting next week.
  

Be careful with hope: it can suggest that you have no control over a situation.

Rephrase and make the situation clear:  

• Here are the samples you requested.   
  
• I hope the meeting goes well and see you tomorrow. [used to signify encouragement]

Be careful with think: it can reduce the power of your speech and make you look unprofessional or inept.

Replace with a positive verb:

• These products are unsuitable for you because your requirements are different. Therefore, we need to make some changes to better reflect your needs.
• I think it’s a good idea to ring the client tomorrow morning and check they fully understand the figures.
  

Be careful with guess: it can convey tentativeness, lack of confidence or incompetence. Informally, it is used to indicate that although one thinks or supposes something, it is without any great conviction or strength of feeling.

If you are unsure, say so and follow with how you will solve the situation:

• These are the preliminary figures. The complete numbers will be with you by the end of the week.
  
• I will ring the client tomorrow morning and check they fully understand the figures.
  

Be careful with want: it could indicate desperation and lack of confidence.

Rephrase to show confidence and do not focus on money:

• This conference looks interesting and useful but do you know where to register?

However, used correctly, it can show strength:

• I want to go to this conference; the subject is interesting and it will offer the perfect opportunity to network.
• The weather’s perfect and I want to go to the beach.
  

Be careful with feel: it can be indefinite and make you look weak. Using the verb means to have a belief or impression, especially without an identifiable reason.

Eliminate and show your enthusiasm:

• Let’s work together more often. You have such brilliant ideas! [much stronger]

However, using the gerund form indicates one speaks from experience:

• I’m feeling confident about that meeting this morning, especially after the comments on the waterfront project.
• I have a feeling it’s all just to scare us into lowering our prices.
• It’s my feeling that using these pictures would create a better impression.
  

Be careful with should: it can show weakness, indecision or lack of commitment. In this context the speaker gives the impression of chaos and indecision.

If the meeting is important and your presence needed, commit and eliminate excuses:

• I have a meeting tomorrow.
  

If you need to soften the statement, prefix with I’m sorry:

• I’m sorry but I have a meeting tomorrow.