Underwear as outerwear is a style that began gaining momentum when popularized by Madonna. The slip dress made a particularly big splash in the 1990s, and one way or another, lingerie-inspired fashion has been with us ever since. It's a combination of casual yet elegant, and thus very appropriate for a wide variety of occasions. But you want the look to seem purposeful -- not like you forgot to get all the way dressed. Some smart styling choices will convey the message you mean.
Chunky shoes balance out the wispiness of a lingerie-inspired dress -- they add heft in a good way. You can choose stacked heel sandals, wedges, even high-top sneakers. Platforms are another solid choice. Or, hearken back to old-school punk-rock inspired style and wear combat boots underneath -- in any color you like, not just basic black.
Try a cardigan up top to add balance to this look. You could choose an oversized boyfriend-style sweater if you like for a shabby chic sort of vibe. Alternately, you can wear a cropped cardigan or even a shrug for a more formal look. Either way, you'll appear more put-together than with your shoulders left bare.
Similarly, a tailored suit jacket or blazer can add the touch of formality needed to make your slip dress work outside the bedroom. Suddenly you've got an outfit ready for any sort of evening affair. You can also try wearing a denim jacket over your lingerie-inspired dress for more casual afternoon events. On the other hand, if you want to up the glam factor, try a slip dress with a faux fur coat.
You won't look like you just rolled out of bed if you style your hair in an up-do, even if it is a messy one for a casual ensemble. A sleek bob or similar style works well with a slip dress too. Avoid messy bangs or unkempt longer hair.
Tone Down Accessories
Go for subtlety when it comes to your accessories. In this case, big statement jewelry will overwhelm the delicacy of your dress. A simple chain, a shiny clutch, and a ring or two are all that's necessary. If you're walking the red carpet or attending an otherwise glamourous occasion, you can get away with more of a statement necklace. Keep in mind that everything else, from your shoes to your jacket, should be toned down as to not compete with your larger jewelry piece.