I'm trying to get my house ready to sell, so my days have been filled with trips to Home Depot and forays into overloaded closets. I am living in my yoga pants these days, and I'm remembering why I love them so much. But I'm also thinking, quite a lot, about the rules for yoga pants--how to wear them, how NOT to wear them, and what to wear with them.

Yoga pants are the new sweats; you can wear them pretty much anywhere, even if you've never done a Down Dog in your life. However, the general acceptability of yoga pants doesn't extend to poorly made, ill-fitting sweatpants. Do not, under any circumstances, buy those polyester-blend sweatpants with the elastic at the ankles. Just thinking about them makes me itch. Get yourself some proper yoga pants, or at least some sweats with wide legs. (Old Navy Just Lounge pants, $12.99.)

Only wear sweats or yoga pants that fit PROPERLY. Be honest with yourself, and choose wisely. No one should be able to tell what brand of underwear you are wearing under your yoga pants. Think, too, about the waist band; yoga pants come in drawstring and flat waists, and will hit everywhere from just above your belly button to just below your hipbones. Pants with a drawstring waist can be more forgiving across the backside than those with an elastic waist. A slightly lower waist--say, just below the belly button--is the most universally flattering; if the waist is too high, your backside will look bigger, too low and your stomach will hang over. It's worth the effort to find yoga pants that fit properly; there's no reason you can't look respectable when you're running out for milk. (Drawstring pants by Gaiam, $34.00.)

Do not wear your husband's or boyfriend's university sweatshirt with your yoga pants, UNLESS he wears the same size you do AND you graduated from said university recently. Like this year. Oversize sweatshirts will make even the tiniest woman look huge. Wear a hoodie or sweatshirt that fits properly, one that hits at your hip and doesn't balloon out at the waist. If you want to advertise your alma mater, that's fine, but do it in something that fits. I suggest, though, that you pair your yoga pants with a nice casual sweater; I wear mine with my cashmere crew neck and a tee that's longer than the sweater, to keep my midriff covered. (C19 by Champion jacket, $34.99, available at Target.)

Yoga pants need athletic footwear--sneakers of some sort, or flip flops if you must, but not in the dead of winter, unless you live in California or you've just had a pedicure. Although I am compelled to add that I know a VERY hip woman who wears her leopard-print Dansko clogs with her yoga pants, and it looks hott. But please, don't try to dress your sweats up with some cute ballet flats. Just don't. (Berne Mev Dina flats, $49.99; this particular pair is sold out--sorry!--but Berne Mev's are the most comfortable shoes you will ever own. Keep your eyes peeled for them.)

As with everything else in your closet, get rid of your yoga pants and sweats when they start to look worn. I can guarantee that the ONE day you run to the grocery in the pants with the hole in them, you will run into someone you really want to impress. Don't take chances. You will look--and feel--better if you're running errands in clothes that fit properly, even if they are the most practical of all practical pieces.

Susan Wagner writes about fashion at Friday Style and about everything else at Friday Playdate. Send her your style questions at fridaystyle.susan AT gmail DOT com.