When trying to achieve a somewhat casual look, oftentimes your inclination will be to don a pair of denim trousers. If properly tailored and cuffed, denim trousers can be an excellent addition to your ensemble, and offer you an intelligent medium between the worlds of semi-formal and casual, however as they say, the devil is in the details.
I must insist that you follow these rules:
Make sure your trousers are tailored to your body. While there are many different fits of denim, for a tailored look you must stick with a slim/straight up-and-down fit with no flare.
Choose dark denim over a light wash every time. The point of your trousers is to anchor your outfit, so a darker denim will always provide a more stable anchor, especially in a corporate setting.
Press your cuffs. If you intend to pair your denim with a jacket or blazer, make sure the lines of your cuff are as clean as possible, even if that necessitates using an iron.
For a more casual look, cuff your denim an inch above the top of your shoe. For a more elegant approach, allow the cuff to rest upon the shoe, and cover your ankles.
As with any look, experiment and find out what works for you, but unless you are on a yacht or enjoying an island getaway, never, ever haphazardly roll your denim as with the photo embedded below.