Breaking in a new wood clarinet is important to avoid damage to the instrument. Wood clarinets, like all things made of wood, expand and contract with temperature and humidity. Wood products that expand too fast risk cracking.
Most wood clarinets are made out of Grenadilla wood, also known as African Blackwood. Grenadilla is an exceptionally hard and resilient variety of wood that is often used with musical instruments. Regardless of the hardness, all wood is prone to cracking or splitting when introduced to heat and humidity.
Upon receiving a new wood clarinet, it is best to allow the instrument to rest for at least 24-hours in its new environment. Instruments are often in airplanes, trucks, and sometimes left on a front door prior to the box being opened and may have already suffered climatic extremes, which is why allowing it to acclimate to its new home is a great idea.
After the instrument has settled in, you should approach playing it slowly and gradually. The first time you play the instrument you will be introducing a lot of moisture and heat. You should play no longer than five minutes the first day. The next day you can double that and play for about ten minutes, the next day fifteen, and so on until you are where you want to be. Overall it should take about a week to properly break in your new clarinet.
Once the clarinet is broken in it will retain its moisture for several days, so if you play on a regular basis you need not be concerned. However, if you experience a prolonged period of not playing, to be safe you should once again perform the break in procedure. Clarinets will dry out over time if they are not played regularly.
Bore Oil is available for clarinets, but should be used cautiously. While the inside of the clarinet can be coated with bore oil, too liberal of an application can leak out of tone holes and onto the sensitive pads. Oiling the bore of the clarinet helps to prevent the wood from drying out and decaying over a long period of time.
When traveling a clarinet should never be left in a car, or outside, or any place where extreme temperature changes can occur. If for some reason you do forget your clarinet in the trunk of a car on a cold winter night, always follow the break-in procedure again to be safe. Blowing hot air into a cold instrument will almost guarantee a crack in the wood!
Lastly, the above is just a guide, there are many other opinions and ideas as to how to properly break in a wood clarinet, and even with the utmost care an instrument could still potentially crack, but following all of these steps will greatly reduce the chances.