The holiday season for online shops is expected to be even brighter this year. Just make sure you’re set for the onslaught.

Forrester's annual U.S. holiday forecast was released today with positive predictions for online holiday shopping. The report estimates sales will grow 15% from 2012 to 2013, which amounts to nearly $79 billion.

The increase means online retailers should be optimistic, but they’ll also need to be prepared to make a few tweaks and sacrifices.

First, online retailers need to make sure they have mobile apps and websites that can handle the influx of shoppers browsing and purchasing. The report indicates that price and discounts will, as normal, be the primary motivators for consumer purchases, but retail ecommerce professionals must also ensure there is a quality set up to attract and support mobile shoppers. According to the recently released Annual Holiday Survey from Deloitte, a retail and distribution consulting firm, nearly 68% of smartphone owners will use their devices for holiday shopping this year. Ensuring your platform can sustain the influx of shoppers, will be crucial to maximizing your holiday revenue.

The report also predicts that business owners can count on continued effectiveness of tried-and true holiday promotions like free shipping, promotions towards "hot" days like Cyber Monday, and constant, promotional emails.

While these methods are effective, businesses should be aware that free shipping is becoming a necessity. As customers grow to expect it, businesses must be willing to sacrifice the extra profit coming from shipping charges to keep customers shopping until checkout.

Zappos and Amazon are just a few of the well-known companies setting the precedent for free shipping. Small businesses must offer it too if they want to compete.

“Many consumers will actually leave a site if it doesn’t offer free shipping,” the report reads. “It’s the second most common reason (behind price) why U.S. online buyers abandon purchases and go to another retailer. Moreover, shoppers may never make it to your site if you don’t offer it; Google Shopping now allows its users to sort search results by retailers that offer free shipping.”

The upside? When free shipping is offered, customers might buy items they didn't originally intend on. The longer you keep shoppers feeling positive about what your business offers, the greater your chances are that they’ll keep buying.