Taming your cockatiel makes cleaning and caring for her easier on you. It also makes handling less stressful on the bird since she will not be scared when you hold her. If your bird must visit the veterinarian, being well tamed will make the process nicer for everyone.
Allow her to become accustomed to her new surroundings if you are just bringing her into your home. At least a half-hour of peace to adjust is necessary, although longer is better. If her wings are not already clipped, have them clipped so she cannot fly away and injure herself.
Place her cage near you so she becomes accustomed to your presence. Sit quietly near her at every opportunity. Sing or talk softly, but make no attempt to open the cage door or approach her. Do this for several hours, or even several days until she is comfortable approaching the side of the cage nearest you.
Begin offering small treats held in your fingers through the bars of the cage. Do this several times until she is comfortable taking the food from your fingers.
Open the cage door and sit in front of the cage. Be sure that all doors and windows are closed and all fans and heaters are off before opening the door. Hold a small treat in your fingers and talk to her softly until she approaches to take the food. Continue doing this for several days.
Place your hand under her, in front of her legs. Move quickly so she does not have a chance to see you coming or to bite you. Once she steps up onto your hand, hold it still and give her time to adjust. Let her step off when she's ready, and leave her be for awhile. Continue this process until she willingly steps on your hand when it's placed in front of her. Once she is comfortable with this, you can begin moving around while she is perched on your hand.