A texturizer can help to make a thick head of hair more manageable. However, anytime you plan to put chemicals on your hair, it's important to get it to its healthiest state possible. Once you apply a texturizer or perm of any kind, the chemistry of your hair is altered and significantly weakened: So going in with strong, healthy hair from the outset can help to prevent damage.
Apply a deep conditioner to the hair leading up to the date of the relaxer. Conditioners not only help to restore moisture to the hair shaft, but leave it more manageable overall. This will reduce the need to "handle" your hair with styling tools. The less stress you put on your hair before the texturizer, the better.
Reduce use of heated styling tools. Flat-irons, blow dryers and other heat styling implements cause the most damage to your hair. By greatly reducing your use of them before and after the texturizer, you give your hair a chance to recover a bit before applying a box full of chemicals to it.
Wear hair loose as much as possible. Ponytails and other tight styles cause damage and breakage to your hair. Try to leave your hair down when possible, even if this means cutting and shaping it into a more maintenance-friendly hairdo, such as a bob or wavy shoulder length style.
Keep hair clean to stave off scratching. Anytime you apply chemicals to the hair shaft, you run the risk of irritating the scalp. This is even more pronounced when you scratch a dirty head just a day or two before applying a texturizer. Wash your hair a few days before and make sure to condition it well, so your scalp doesn't get dry.
Apply sunflower oil to your hair just before applying the texturizer. The oil will lock in some of the hair's natural moisture, which is sapped by the texturizing process. You should also line your forehead, neck and around your ears with Vaseline to avoid any chemical burn.