Plain and simple: Good job references are like precious gold jewelry. Treat them with great care, career experts advise.

One of the last duties a human resources professional or recruiter will carry out is reference checking, and the impression your references give about you can be more significant than you might have thought--especially in a tight economy.

The last thing any of us wants is to lose out on an excellent job opportunity because a reference we thought was solid turned out to be sour. And they can be sour.

"Our firm hears poor to bad references on a daily basis," said Heidi Allison, managing director of reference-checking company Allison & Taylor, in a statement on reference etiquette.

Allison also observed, "In today's highly competitive job market, people pay so much attention to their resumes and interview skills, but unfortunately, many fail to nurture their professional references, and they can make or break a successful job search."

Allison & Taylor has some advice on the best etiquette for handling job references, suggesting a five-point plan for effective reference management.

1. Call your former bosses and ask them if they are willing to be good job reference for you. Be sure to thank them for supporting you in your job search if they agree.

2. Let them know each and every time you give out their name and email address.

3. Keep your former positive references informed of your experiences in climbing the corporate ladder and your educational progress. Give them a career update. He/she will be more inclined to see you in a stronger light as you progress.

4. Spending time with a potential employer is taking valuable time out of your former bosses' days. If you plan to use these positive references over the years, you need to give something back. For instance, after receiving a good job reference, write a personal thank-you letter or (at a minimum) send an email. Better still, send a thank-you note with a gift card for Starbucks, or offer to take your former boss to lunch/dinner.

5. If you win the new position, call or email your former boss and thank them again for the positive references. Also, let them know your new contact information.