Many bicycle commuters bring the bike into their building, and store it either in or near their workspace, or in a closet or storage room in the building. Mounting a hook to hang the bike on the wall, either by the frame with the bike flat, or by the front wheel with the bike hanging down, is a great space-saving solution.
Occasionally, employers give you a hard time about keeping the bike in the building. If this is the case, take stock of the benefits to your employer; after all, they probably provide automobile parking for others. Be sure scout around for an empty corner or a good spot for a bike rack, so that you can address your boss armed with some specific suggestions.
Others lock up their bike near a guardpost or gas station. Try to find somewhere supervised to keep your bike. If you have to, locking it to a bike rack or a seriously immovable object will suffice, but you'll want to use both a chain and cable lock if you work in a crumby neighborhood. Don't skimp on locks if you are leaving your bike every day -- read about choosing a lock, using a lock, and more in our bike theft section.
Use an expensive U lock, and when you unlock your bike, click the lock to the bike rack at work. Coil up the cable lock and store it on your bike in case you want to stop for a donut, as a cable lock is much lighter and compact than a quality U lock. Make sure that your U lock is made of case-hardened steel, and that the locking mechanism is not at the end of the cross bar, and that you leave as little open space within the U as possible.