This nice tip on "Issuing Commands" to improve voice recognition accuracy comes from Dragon NaturallySpeaking e-letter.
If you’re telling the computer to do something, and it doesn’t seem to be listening, or simply isn’t completing the right task, the problem could be the way that you issue your commands.
Pause briefly before and after saying all commands. Dragon uses the length of the pause between two utterances to determine whether you are saying a command or dictation words. Do not pause, however, before saying dictation commands, such as "Cap", "New-Line", or "New-Paragraph." You can change the length of the pause that Dragon recognizes to identify a command. Under the Tools menu, click Options and click the Commands tab. Also, be sure you are saying a valid command. You can open the Command Browser within the Tools menu of the DragonBar and perform a search for that command to see if it is valid.
If you’re still having a problem, hold down the Control key as you start to say the command. This hot key disables dictation and forces Dragon to recognize what you say as a command. You may also consider training voice commands that are often mistaken for dictation to keep the problem from recurring. Simply click Train on the Words menu of the DragonBar and enter the command you want to train.