Design prompts, and especially reprompts, that anticipate typical user errors
When you can foresee a possible problem, including how to fix it in the instructions can be what makes a dialog state successful. In most cases, you'll want to keep initial prompts as concise as possible and put the anticipation in the reprompts.

• Initial: Say or enter your account number.
• No Input: Your account number is in the blue box at the top of your statement. To continue, please say or enter it now.

For another example, if you anticipate that the caller will need to get information that they have not memorized, either provide a long enough timeout for them to locate the information (e.g., time to get a credit card out of a wallet or purse – usually 10-15 seconds will suffice for this), or provide functions to pause/resume the application.

Or maybe the account number is printed like 123456789-0. Is the zero needed? Will is cause a problem? Do you say the dash? You will get all sorts of responses to “say or enter your account number” in this situation. One solution is to write grammars to accommodate all possible formats and then deal with it, but you can also do with it the prompts.

• Say or enter all the digits of your account number before the dash.