"I was alone in the elevator with the hiring manager for a temp-to-perm job I really needed," recalls temp Ben Whittle. "I knew I should say something -- anything -- to make the case for picking me. But I was nervous. I didn't want to sound stupid, so I opted to say nothing. I missed a great opportunity and ended up not getting the job."

How many times have you been unable to find the right words in an impromptu situation like this? Selling yourself on command can be tough, particularly when you have to do it in a short time period. This is why you should develop an elevator speech, or a sound bite that details your professional story, before you need it. Follow these five pointers to craft it.

1. Focus on Why You Want the Job

Think about why you want this job, and write down all your reasons. Delete anything that could apply to most candidates, like "I need the money" or "I want to work in this industry." Look for personal, unique reasons why the position is right for you. If you like a company's corporate culture, be sure to mention it. If the position will enable you to achieve a professional goal, focus on that.

2. Consider How You Can Contribute

Again, steer clear of stock answers in favor of those that showcase your one-of-a-kind skills and attributes. Explain how you could benefit the bottom line or fill a skills gap.

To tailor your responses to individual situations, be observant. For example, "I was waiting for an interview at an accounting firm when I noticed the staff was having trouble communicating with the firm's Russian-speaking clients," says contractor Marta Damien. "So during my interview, I told a story about studying Russian in college. I got the assignment."

3. Be Honest

You want to sound good but not too good, cautions Catherine Conant, a professional storyteller and consultant. "Don't try to make yourself bigger, braver, richer, smarter or fancier than you are," she says. "People have an incredible ability to spot a phony. Only tell stories that contain the truth about what you know about yourself."

4. Keep It Short and Focused

Since you'll be delivering your pitch in a compressed time frame, include only the most interesting and relevant information. Think of the amount of time you spend in an elevator -- usually no longer than a minute.

"People are busy, and the last thing they want to do is listen to someone ramble on about getting a job or plum assignment," says former temp Sally Ross. "When I decided I wanted to work full-time at the law firm where I was temping, I spent some time figuring out what my bosses cared most about so I could do it quickly and effortlessly.

5. Practice

When you've figured out what you want to say, Conant suggests these tips to refine it:

• Say it out loud, and make some notes about what you want to improve or remove.
   
• Vary your tone of voice, and use natural gestures and body language. Remember, people gather much of what they know about each other from nonverbal cues.
   
• Rehearse so you're comfortable, but don't write it down and memorize it. This will make it sound forced, and if you forget something, you'll panic. 
   
• Lastly, ask friends to critique your presentation. "That will help you discover what the listener needs to hear more of and what's too much information," Conant says. Your friends can also tell you if your gestures look natural. Proper preparation also increases your comfort level and helps calm your nerves.