1. Return your customers and remember them about your store - send them the re-activation letter, offer some kind of bonus or discount. You can use Abandoned Cart and Wishlist Reminder add-on. Besides, this add-on can be used for working with forgotten carts and wishlists.
2. Increase the average order sum with up-selling and cross-selling. For example, offer the free shipping for orders of fixed total. The Free shipping notification add-on will inform your customers about the sum left to get the free shipping. Persuade your customer, that it is more profitable to purchase several products (for example, Product package) than one item. Another option is to offer accompanying products (accessories, covers, chargers, etc.) The Additional products add-on is used for placing extra products with opportunity to add them into the cart exactly from the the detailed main product page.
3. The seasonal calm is a good time for customer-interesting programs and events: sales, new products, new payments and shipping methods embedding. The main point is to inform your clients with any suitable methods: send messages, post blog articles, add banners, pop-up notifications or for example special labels to the products.
Do not forget about new clients. Of course, there are less new clients, but they still come to your store. The good design is not enough. The store should works correctly and it should be easy to use. For example, to find products fastly with Live Search, to find additional information with in FAQ, to place order on one page with One Step Checkout, etc.