How can you improve your credit score?
It's virtually impossible to change your score in the time between when most people decide to buy a home or refinance their mortgage and when they apply. So the short answer is, you really can't do so "on the spot." But there are strategies you can live with to make sure when you apply for a loan your score is as high as possible.
Make sure that the information each of the three credit reporting bureaus has on you is consistent and up to date. Order a copy of your credit report about once a year, and dispute any inaccuracies.
Note: Theoretically, if a series of credit reports is requested on your behalf...