Bathtub could likely have a lot of dust and hair. If that's the case and it's dry, the best way to remove is by vacuuming or using a dry towel. The tub needs to be free of hair and dust before you apply product.
Spray Tub & Tile Cleaner from to bottom on bath tub. Make sure tub is dry before you spray.
The reason we spray top to bottom is that the dirt is falling downwards as the cleaner sets in. Let spray sit for 5 minutes.
Use a thick sponge or scrub brush to clean from side to side, top to bottom.
Pour water into a small container and wet the sides of the tub.
If there are any rust stains or yellow spots, mix baking soda and Seventh Generation Dish Soap to make a paste (the consistency of tooth paste). Apply to the spots and leave for 10 minutes. With a pumice stone, rub the paste in a circular motion. Splash with water from a small container.
If there's any mold in the tub, directly apply Tub & Tile Cleaner. Let sit 10 minutes. Clean with a scrub brush very strongly. Splash with water from a small container.