Practice proper breathing techniques for singing. As air moves across your vocal chords and causes them to vibrate, sound is produced. Therefore, without a proper breath of air, the sound may weaken, which may result in scratching. Use breathing exercises and learn how to properly intake air while singing. For example, one exercise instructs you to imagine sucking air through a straw and feeling your diaphragm fill with air. Your shoulders should be relaxed with your chest out. As you draw in the air, become in tune with how your lungs fill with air and your diaphragm rises. Practice other breathing exercises recommended for singing as well.
Employ proper vocal warm-ups. Just like you need to warm-up before physical exercise, it is imperative you warm-up your vocal chords before singing. Otherwise, they may be shocked as they are asked to produce sound and may not vibrate properly as air moves over them producing a scratching sound. For example, one basic warm-up is humming. Place your tongue against the back of your bottom teeth with your mouth closed. Making a "mmmm" sound by pursing your lips, slowly move up and down scales within your vocal range. Remember to employ proper breathing techniques and posture.
Refrain from smoking and alcohol. Smoking and alcohol consumption affects your vocal chords in several ways. It dries and irritates the tissues of the larynx. It may cause acid reflux where stomach acid travels back up the esophagus and into the larynx, also irritating the chords and surrounding tissue.
Consult a throat specialist. Some scratching of the voice may be occurring from nodes which have developed on your vocal chords. Nodes are formed due to several factors, such as improper singing technique. If diagnosed, the specialist will prescribe voice therapy and medical treatment to alleviate the nodes. It is rare that a surgical procedure is needed to correct the nodes.
Become conscious of when you are straining your chords. The moment you hear your voice begin to scratch, stop and readjust how you are singing in terms of posture and breathing. Additionally, refrain from feeling as if you need to "push" the sound, as that causes stress on your vocal chords as well. The more you sing properly, the more you'll feel when you are not stressing the chords and can adjust accordingly.