Sheath dresses and other fitted styles are one of the most difficult items to buy (at least for me). There's almost always at least one spot where the fit isn't quite right. Here's how to tell if you've found your perfect fit.

Could I be more in love with this sheath from White House, Black Market? Probably not. Love it!!!!

The neckline should lie flat across the top, without pulling or gaping. The model, left, shows a perfect neckline--see how the lace lies flat across her collarbones?

The bust should have enough room for the girls. If the dress is mashing them in or if you see pulling across the chest, the dress is too tight. If it's sagging, the dress is too loose. If the dress has darts, they should line up at the center of each breast, not above or below.

The armholes shouldn't constrict movement or dig into your delicate underarm skin. There should be enough room for you to move your arms comfortably, but not so much room that your bra shows.

The waist should be slightly fitted, without pulling or bunching up. Check the back view to be sure there's no pulling from that angle.

At your hips, the old "pinch an inch" rule is the one to follow; pinch an inch of fabric. If there's not an inch there, the dress is too tight; more and the dress is too big. Also, check to make sure there's no pulling across your thighs.

The best hemline is an inch above the knee, though right at the knee can work as well with the right shoes (e.g., sky high heels). Avoid styles that drop below the knee; in a fitted sheath dress, the look is dowdy.