The best way to get your loved one the diamond ring she'll love and cherish for always is to let her choose her favorite diamond ring herself. But if you are worried she'll pick out a ring with the biggest diamond in store or you simply want to get down on your knees and surprise her with that big question, then the second best thing is to choose for her.

Buying a diamond engagement ring is pretty tricky since you are a man. Here are easy guidelines for you to follow before heading out to a jeweler's in town or visiting an online jewelry store. Just make sure you're well-prepared and know how to buy a diamond ring before you really buy one.

1. Do you know what kind of metal does she like to wear? - Every woman is different. While some prefer gold jewelry, others adore white gold and platinum. Have you noticed her jewelry? Is her necklace in gold or silver color? What about her earrings and bracelets? If they're all the same, and she kind of wears them all the time, then that's her favorite. So, when you buy her a diamond ring, you'll have to look at either the ones in gold or the ones in white gold or platinum. Note that white gold is cheaper than platinum. It will be a lot easier for you.

2. Is she an adventurous, a classic or a contemporary woman? - You must know her. After all, she is the one you love, isn't she? If you can summarize her in one word? What's she like? Is she funky, edgy, eccentric, shy, old-world, self-confident, dare-devil, outspoken, conservative, elegant, urban, modern, sexy or what? Is she an Angelina Jolie in Tomb Raider, an Audrey Hepburn in Breakfast at Tiffany's, a Sarah Jessica Parker in Sex and the City, or a Jennifer Aniston in Friends? Keep this in mind when you pick out a diamond ring for her. The diamond ring must portrays her style.

3. Notice her hands and fingers: Are they short and chubby or long and sleek? - This is an extremely important factor. If she has short and chubby hands and fingers, then the best choice would be an elongated diamond like a marquise or an oval because it will make her fingers look longer. If her hands and fingers are long and sleek, then you would have no problem at all. Any diamond will look good on her. Now about the band. If the band is thick, it will make her fingers look shorter. On the contrary, if the band is thin, it will make her fingers look longer.

4. Do you know what shape of jewelry she likes? - While round diamonds are the most popular shape of diamond, it is very important that you pick the diamond shape she likes the best. You can always tell by looking at the jewelry she wears every day. Is it round, pear-shaped, square, or cluttered? Do you think she'd prefer a solitaire diamond engagement ring (a diamond set alone in a ring)? Or do you think she'd perfer a cluster of diamonds? If you take a good look at her everyday jewelry, you'll have a pretty good idea.

5. What ring size does she wear? - You can ask her mother or her best friend. If they don't know, they'll figure a way to find out.

Keep in mind that a diamond ring is the most important ring in her life. Spend some time to learn about her style and you'll buy the most beautiful diamond engagement ring for her. If you get it right, she'll love it, not because she has to, but because she wants to.