There are already plenty of simple plugins that let you offer coupons to your visitors to encourage them to buy more from you. The WooCommerce Extended Coupon Features Extension lets you create more sophisticated discount rules or simply give away free products.
Thanks to this plugin, you can automatically apply discounts to the user’s cart if your conditions are met or via a URL. You can also offer customers free gifts to choose from. Webmasters have the option to restrict coupons by shipping/payment method and product combinations.