The fundamental thing is to play on the concept of "pamper yourself, on Valentine's Day" , inserting in the email beautiful photos that encourage them to try a massage - in the case of a beauty center - or a strengthening treatment for hair or "a blow-dry to make you beautiful" - in the case of a hair salon.
Tip: also include the price of the treatment, for example select 2 treatments with a slightly higher cost and 2 treatments at a more affordable cost.
Here is an example of a Valentine's Day email from a beauty center.