ameliorate/improve

Keep in mind that to ameliorate means to alleviate or mitigate something painful or bad. Similarly, to improve means to bring something into a more desirable condition, suggesting that it was less desirable before. Take a look at the following examples.

• We’re taking an extreme effort now to make sure that we reach a resolution because we are more and more sinking into a deficit situation that we may not be able to ameliorate, and I’m not just going to sit around and let this situation overwhelm the taxpayers of New York (New York Times, May 4, 2010): The author is trying to ameliorate a budget deficit, which is generally considered undesirable.
  
• The Indigenous HIV/AIDS Research Training program, designed specifically for indigenous and other underrepresented ethnic minority scholars, mentors and trains the scholars to design culturally grounded research that will contribute to ameliorating health disparities among American Indians and Alaska Natives in the areas of HIV/AIDS, other sexually transmitted infections, and mental health (Kimberly Teehee, "Together We Must Face the Challenge of HIV/AIDS in Native American Communities", March 19, 2010): Kimberly Teehee argues for ameliorating health disparities, which is also not a good thing to have.
• Europe's economic prospects are improving slightly, despite worries about government debts and persistently high unemployment (Wall Street Journal, May 5, 2010): By saying "improving," the author implies that Europe's economic prospects have not been so bright.
  

Therefore, when you are talking about a situation that is not necessarily undesirable, do not use "ameliorate" or "improve." The following sentences are some of the mistakes that I have seen very often.

• To strengthen its relationship with the U.S., Korea should renew the mutually beneficial trade agreement: If you said "improve" instead of "strengthen," it would imply that the relationship hasn't been very good. By saying "strengthen," you suggest that renewing the agreement makes the relationship even stronger.
  
• By successfully managing routine multitasking, employees can refine their judgment about information: If you said "alleviate" or "improve" instead of "refine", it would mean that employees didn't have good judgment. By saying "refine," you simply suggest that employees will have even more precise judgment.