Ah, the holiday season. The lights are aglow on both the Christmas tree and the laptop. This holiday season, U.S. consumers are expected to spend as much as $117 billion shopping online, according to the National Retail Federation. That's an increase of up to 10 percent from last year.

As consumers are poised to spend more, it's now up to your business to attract and convert new clientele. By giving shoppers what they want most, you will already be well on your way.

The next key to drastically increase your online sales this season? Recover purchases that were placed in the cart but not bought.

Think about it. You were already so close. This shopper heard about your business, went to your site, found an item he/she liked and added it to the cart. A few more clicks, and this would have been a success story. What happened?

Likely, your checkout process was too long, complicated or unintuitive. Shoppers most often abandon their cart at the payment stage, checkout login or when they need to enter their billing or shipping info, shows an Internet Retailer study.

All of those nearly-there purchases add up. Retailers are expected to miss out on $4.6 trillion in sales in 2016, shows Business Intelligence data.

But there is good news here. About 63 percent of those abandoned purchases can be saved. And email has been proven to be one of the most effective ways to capture and convert abandoned purchases.

Read on to learn how to write a powerful email to shoppers who abandoned a purchase and convert them once and for all.

1. Act quickly. Send the first email three hours after the customer left the cart. These emails get an average open rate of 40 percent and click-through rate of 20 percent, found Listrak data.

2. Personalize. Show, don't tell, your shoppers what they're missing. The copy of this email should be short and sweet. Instead, focus on the products they left behind. When you include images and info about the abandoned items, you'll get 25 percent higher transaction rates, shows Experian data.

3. Make it easy. Your goal is to propel your reader to action. Include a straightforward, prominent call-to-action button. 78 percent of retailers go with "Checkout Now," shows data. That's likely your best bet, too.

4. Try and try again. One email simply isn't enough. Your business should send at least two and up to four abandoned cart emails.

5. Incentivize. Hold onto your discounts and freebies as long as you can. They're your last card to play, so wait until at least your second or third email. Most commonly, businesses share a 10 percent off promo code, shows a study. While most common, percent-off discounts aren't the most successful. Instead, dollar-off offers propelled the highest transaction rates, according to a recent study, followed by free shipping offers.

One email campaign this season could be the boost your business needs.