You can get your teeth noticeably whiter in one day by using lemon juice and baking soda.
Mix some baking soda with some lemon juice to make a baking soda and lemon juice toothpaste.
Wipe your teeth off before applying the lemon juice and baking soda toothpaste to remove excess saliva from your teeth.
Apply the baking soda and lemon juice paste to your toothbrush and apply it to your teeth and leave the toothpaste on your teeth for at least 1 minute for it to be effective and then brush your teeth as normal.
You should see whiter teeth soon after brushing your teeth with the lemon juice and baking soda.