Avoid chemicals,use light oil or leave in conditioner everyday, avoid heat, avoid over brushing,be very careful when using rubber bands and do large loose weaves.
Everyone's hair grows at about 6 inches a year, unless there are medical problems. So your problem is probably hair care. You have to ask yourself some questions. How often do you wash your hair? Do you get the proper balance of moisture and protein to your hair?
If you go to your local target or wall-mart in the section for African American hair there is some products made of olive oil. Look on the back and see if you like whats on the label.
In order to grow African American hair one most wash, condition, and grease the scalp at least twice a week. Use light conditoners and,light greases each time. Keep the hair braid are just combed and brushed. Do not apply heat such as curling irons , pressing etc.. on the hair. Try sulfur 8 and mane and tail conditioners.
Due to it's texture, African American hair has a tendancy to break before getting long. Moisture in key, and keeping harsh chemicals away from hair will help stop breakage, and allow hair to grow.