If you don’t already own a shofar, it’s better to first learn how to blow on a borrowed shofar before buying one. When you do go to the store, you need to find a shofar that is right for you personally. For reasons that are purely commercial, the longer the shofar, the more it costs. But don’t make a choice based on appearance alone; the way the shofar feels and the way it sounds are what count. It’s important to find one that feels comfortable on your lips, since the shape of the mouthpieces varies greatly. One mouthpiece may be too round for you; the edges on another may feel too sharp.
Most shofarot can produce two (or more) notes, a higher note and a lower one. The higher note requires more effort, but is far more attractive and impressive a sound. As you blow, squeeze your lips more tightly against the mouthpiece until you locate the note you want.
Once you have found a shofar that feels comfortable, keep blowing it for several minutes. This is not only to make sure that you are happy with your choice, but also because some shofarot do not have “staying power,” that is, they tend to lose strength after a few minutes.
It’s possible that your new shofar will still have the odor of the sheep from which it comes; this will disappear in time. Some say to wash the shofar out with vinegar in order to get rid of the smell. In my experience, however, this just makes it smell like vinegar. Keep your shofar clean and dry, and it should last a lifetime.