An estimated 1 billion people now shop online, including more than 200 million Americans. "I don't care who you are or what you do, if you own or run a business, you just can't avoid [the internet] anymore," says Rieva Lesonsky, former editorial director of Entrepreneur magazine and current CEO and president of GrowBiz Media and SmallBizDaily.com.

Even so, one in four U.S. small businesses still don't have a website. And many of the business owners who have gone digital are still making critical mistakes harmful to their business.

"Far too many small business owners are still severely under-informed or misinformed about what they need to be doing online," Lesonsky says. "I think many small businesses — particularly Main Street businesses — continue to lag behind the trend. They were slow to build a website, slow to realize people buy online, and now they're slow in adapting to mobile technology."

Many small business owners are resistant to the fact that commerce is moving online. Or they don't think that reality applies to their particular business or industry. Or they're overwhelmed with other tasks and not sure they have the time to commit to building a web presence. Even among the willing, many worry that the cost will be prohibitive. But the fear business owners feel shouldn't stem from the challenge of moving their business online. Rather, they should worry about the price of failing to adapt to the changing marketplace, Lesonsky says.

"Businesses that don't adopt these techniques are going to have a lot harder time getting any bigger. They'll stay small and maybe get pushed out of the market by a competitor that is doing the right things online," she says.

Many businesses need to concentrate on getting better at mobile responsiveness and social media, Lesonsky says. Even among the small businesses that have an online presence, nearly half don't have responsive websites, meaning their sites don't scale properly to fit on smaller smartphone screens. That's a problem, since Google is now punishing sites that aren't responsive, and an ever larger percentage of web traffic comes through mobile devices. Much worse is the fact that customers are not forgiving when they encounter a site that doesn't display well on their smartphone or tablet.

"Research says customers using mobile devices who go to your website and discover it's not mobile-friendly leave the site and never come back. And then they go immediately to a competitor's site," Lesonsky says. "That's not something you want as a business owner."

What about social media? For starters, Lesonsky recommends reserving your name on all the big platforms. "Take it so no one else can. You can always decide where you want to focus your presence later, but that's a critical first step," she says.

Offering discounts and coupons is a great way to track the effectiveness of your social media outreach, Lesonsky says. She also recommends embracing the immediate and direct interactions that social media allows businesses to have with their customers, even on review sites like Yelp.

"I understand why business owners hate Yelp, but it's now the way of the world and you have to play the game. Reviews of your business are crucial factors in peer decision-making and it's better to respond to a bad review with promises to do better than to ignore it," she says.

There are so many details to worry about when it comes to getting results online, it often seems like there are too many to keep straight, says Larry Bailin, CEO of Single Throw Internet Marketing and author of Mommy, Where Do Customers Come From? For Bailin, the number one concern companies need to have online is sales, and the most important factor influencing the bottom line is customer service.

"E-marketing, website design, social media, analytics... Getting caught up in all the details is easy to do. The biggest mistake small business owners make is that they forget to look at them as sales functions," Bailin says. "If you don't keep the larger picture in your head of how you're going to get output from them, all of these bells and whistles mean nothing. Businesses need to understand that people visit their websites to buy, and anything that gets in the way of that is trouble."

Bailin recommends businesses put as much effort into their customers' online experience as they do with the retail experience at their brick-and-mortar locations.

"It's critical to understand the journey the customer takes as he or she shops with you online," he says. "If a person gets to your homepage and has to sign up for a newsletter before seeing any products, how is that any different from greeting them with a clipboard when they enter your store and demanding an email address before you let them look around?"

Bailin gets peeved by cumbersome checkout processes found on many e-commerce sites, and can't stand content that sounds inauthentic or jargon-filled.

"I advise all my clients to read all the content on their website and ask themselves if they would say all those things to a customer who they were meeting in person," Bailin says.

Analytics and other measurement tools can be helpful to a web-savvy business owner, but they're just as likely to be distracting and confusing. The key to winning online, he says, is to treat every single visit to your site as if it will be your next best customer.

"Data on site visits, Google rankings, and conversion rates can be made to look pretty amazing, but never forget that the ultimate measure of your success is sales. If marketing doesn't move revenue and income, it's a loss," Bailin says. "If you're converting five percent of your web traffic into sales, I get pains in my stomach about the other 95 percent. You have to pay attention to every single visitor who touches your brand and make sure they're getting the show you want them to get."

And for businesses who think their web presence is underwhelming? Don't place blame elsewhere, Bailin says. Learn how to make it better, whether that involves doing it yourself, working with your existing contractor, or hiring someone new.

"A lot of people are happy with average online presences and that doesn't work in this very noisy space. No one out there is not using the internet as a buying tool. It wraps around everything we do. Every business has to look at it as a way to get more customers and make more money," he says. "Done right, it will."