You can find a range of hair serums at any department store or pharmacy.
Wash and rinse your hair as normal, making sure to wash all of the soap out of your hair.
Consider doing a “no-poo” routine for cleansing wavy and curly hair. If you are trying to create more natural waves, there are shampoos without cleaning agents that rough up the cuticle and create frizz. If you are planning on only applying the serum to your styled hair, you can skip this step.
Be careful not to use too much serum, it may make your hair greasy and heavy if you do.