Buying a diamond can be an exhilarating but daunting adventure, especially if you're a newbie.

If I could offer only one piece of advice it would be this: "Learn as much as you can about the 4Cs before you go shopping."

For the uninitiated, that's cut, color, clarity and carat weight. And I like to add one more - common sense.

Choosing the perfect diamond (and there's no such thing as the "perfect" diamond, although a few have come close) is as much a matter of personal taste as it is a matter of the diamond's characteristics.

Some couples are willing to forego quality for size, others prefer the brilliance of a flawless blue-white diamond over a larger stone with less clarity.

You be the judge - but not until you're clear about those characteristics I mentioned. I suggest you read our Diamond Buying Guide, or go to one of the quality online jewelers such as www.bluenile.com or www.mondera.com.

Talk to any jeweler and they'll all give you a different opinion as to what they believe is the most important quality of a diamond.

According to Mayer Herz, Vice President of Diamond Acquisition at Mondera.com, "Cut is the most important consideration if you're on a budget. You can make up for low color and clarity if the stone is well cut."

However, Joseph Schlussel, Publisher of Diamond Registry Bulletin, says "I personally believe that color is the most important thing. Most people who go into a store today, they are told about cut. But I look at what you can see with a naked eye. I would put cut the last, because most people can't see it."

The safest all-round bet is to look for the overall "package", with the levels of cut, clarity, color and size as good as you can get for the price you're willing to pay.

Here are my tips to help you get the best value possible:

* Ensure you get a Gemological Institute of America (GIA) or the American Gem Society (AGS) Certificate when you purchase your diamond. A Certificate guarantees that you are getting what you paid for.

* If you are buying at a retail store, ask to see your diamond against a white cloth (or take your own - even a white piece of paper will do the trick!). Jewelers typically use a black felt cloth to display their stones because all diamonds look white against black.

* The American Gem Society says that the cut of the diamond can influence the price by as much as 50%. A well-cut diamond, when viewed from above, will sparkle with a brilliance you won't find in any other precious stone.

* Most diamonds have flaws (called inclusions) that developed during its formation millions of years ago. Some are impossible to see with the naked eye, others glare at you. The more inclusions, the poorer the quality of the diamond, and the less light it will emit. But its all a trade-off - fewer inclusions means a more expensive diamond.

Knowledge is power, and the more you understand about how diamonds are graded and how that determines the price you'll pay, the better you'll be able to judge what is good value.

Above all, remember that you'll be the one wearing it, and hopefully for a long time, so the final decision is yours. My very first diamond had a hairline crack deep inside it, and I came to love that diamond as much for its tiny flaws as I loved my husband for his!