Protect From Moisture
Before your clarinet leaves the factory it has been thoroughly treated in oil, including usually a year submerged in oil. And yet you must continue oiling it. It will not absorb much oil, for it was thoroughly impregnated, but methodical oiling is necessary as long as you use the instrument. The new clarinet must be oiled once or twice a week for the first 3 or 4 weeks. After that, it must be oiled once a month for about 6 to 8 months. By this time it is pretty well saturated with oil and will absorb very little more. Two or 3 times a year are sufficient usually after the first 8 or 9 months.
To oil, soak a cloth with linseed or olive oil, wring out as much oil as you can, and use this as a swab. Attach this cloth to a strong cord with a weight on the other end and pull the oiled cloth through the bore 2 or 3 times. Be sure the cord is strong, for if it breaks and leaves the swab stuck in the bore of the clarinet you're in for trouble. If this should happen, make a wire hook, snag the swab and draw it out the end from which it was inserted.
Take care that the pads over closed holes are covered with little squares of paper to protect them from the oil, as oil will cause the soft skin which covers the pads to become dry and hard. A hard, dry pad will not seal the tone hole effectively. Also check the register hole to be sure your swabbing has not dragged dirt into it and partially closed it. Use a pipe cleaner or feather to clean it out. On articulated models watch also the Cit and Gt hole.
Daily care consists of running a swab of chamois or a piece of old silk through the bore. 2 or 3 times after each playing engagement. This will remove water that has accumulated there during playing and will give it less chance to soak into the wood. Whenever you can, leave the case open so such moisture as is left may evaporate as quickly as possible. It's a good idea to keep a piece of camphor in the case during summer months when humidity is high, to help absorb moisture when the case is closed.
Be sure to take all joints apart. Some cases are blocked to hold the upper joint and barrel joint as a unit. If your case is so blocked, you'd do well to reblock it or get another case, as all joints should be taken apart. The barrel joint particularly is liable to crack, as it is nearest the mouthpiece and gets the most moisture. Taking the barrel joint off also permits the top joint to dry better, and next to the barrel joint it is the one which is most liable to become soaked with water.