Some women have been dreaming of their pie-in-the-sky engagement ring since they were little girls (ahem, a 3.5-carat cushion cut), and know everything from what shape most flatters their dainty digits to how many pavé stones will dot the surrounding bands. Most of us, though, need a bit more guidance when it comes to purchasing a rock.

"Do a little bit of research on the Internet and in stores," suggests Angelina Chen, president of Circa Jewelers. "Remember," she adds, "you'll be wearing this for a very long time."

Gentlemen, we're here for you, too. As far as your wallet goes, "the rule of thumb is [to spend] approximately 30 percent of your annual salary," advises Chen. But with that money, "you can buy a 10-carat stone that is terribly flawed or a beautiful 2-carat one," she adds. Educating yourself and understanding fundamental diamond basics like the four C's of diamond buying will help you make the most of your budget.

Cut

There are two basic cuts when it comes to diamonds: a step cut and a brilliant cut. But don't get confused—the cut specifically refers to the way a diamond was actually made and faceted to allow light to reflect from it, whereas saying a "round cut" just refers to the diamond's shape.

Over 75 percent of diamonds sold go toward engagement rings, and the vast majority are brilliant cuts. "All of [the] pavilions are sharp and should be facing down," says Chen. But be careful: "If there are too many facets, it may detract from the overall shine," she explains. Brilliant-cut shapes include round, princess, square, oval and heart-shaped diamonds.

The alternative is a step-cut diamond, a Victorian-era trend that's recently made its way back onto the engagement ring circuit. Shapes include emerald and Asscher-cut diamonds. While step-cut diamonds are less radiant, you'll get more bang for your buck when it comes to carat weight.

What is probably the most amazing detail about both step cuts and brilliant cuts are that they share something so unique: "Both should ideally have 58 facets each," says Chen.

Carats

Not sure whether to opt for the bigger rock? Keep finger size in mind. Carats are tricky because small subtleties affect the price, even if the difference in size is nearly imperceptible. For example, there can be a large difference in cost between a 1.79-carat and 2-carat diamond. "A lot of it has to do with marketability," she explains. "A 2-carat stone can look extremely gaudy on someone with very thin fingers," Chen says.

And watch out for a stone whose cut has been compromised in the name of carat weight; cheap jewelers may cut too deep or shallow to make for a bigger stone. Though the carat weight will be higher, your diamond won't sparkle the way a properly-cut stone would.

Color and Clarity

When it comes to stone color, colorless diamonds are the gold standard. Jewelers grade diamond color on a scale from D (colorless) to Z (light yellow). But can you really tell the difference? "D, E and F [grades] are all extremely close [in shade] and are indiscernible to the naked eye," says Chen. Of course, if money is no object, Chen recommends going for the top-of-the-line D-colored stone.

Got a flair for the unique? Try bold colored diamonds. Anything more yellow than a Z is considered a colored canary diamond, and is categorized separately along with other stone colors like celebrity favorites pink and blue.

As for clarity, diamonds frequently have inclusions, or small flaws, including air bubbles, scratches and mineral deposits inside the stone. The less inclusions a diamond has, the more valuable and beautiful it is. A flawless diamond is graded an F, but it is often hard to see inclusions with the naked eye, so this is the one "C" you can skimp on without sacrificing style. In fact, the difference between clarity grades is often a matter of the magnification level on a microscope.

Grades include Flawless (F1); Internally Flawless (IF); Very, Very Small Inclusions (VVS1-VVS2); Very Small Inclusions (VS1-VS2); Small Inclusions (SI1-SI2); and Imperfect (I1-I2-I3). There are plenty of stones that fall between Very, Very Small Inclusions and Small Inclusions that are true investment pieces, but skip out on diamonds graded Imperfect.