Make it highly likely that your customers will tell other potential customers about you.
Hypothetically, this could be all the marketing you require. But don't do it just because it might mean you can Cut your ads budget.
Do it because it forces you to Talk to customers , and talking to customers is fun.
Also because increasing word of mouth marketing is a way to Seek win win wins.
When you've succeeded, you've created a situation where customers gain social status (and maybe some kind of bonus) by recommending you, someone else gets their decision process simplified and their problem solved by you, and you get more customers. Win win win.