The growth of the US digital video advertising industry is unmistakable: Between 2018 and 2021, it will increase by double-digit percentages annually, topping $22 billion by the end of that period.

The industry is also gaining in complexity. Each year brings new formats, devices, platforms, ways of transacting video ads and, accordingly, new best practices.

Some of the best practices industry experts shared in early 2017 continue to be top of mind, including focusing on short ads, front-loading branding elements, using detailed targeting criteria and making ads contextually relevant to the space around them.

Other best practices have taken hold over the past year, in areas such as out-stream video, brand safety and fraud reduction. Some of these were in response to specific events and trends that unfolded in 2017.

"Connected TV advertising will be a big focus for 2018," said eMarketer principal analyst Paul Verna. "The audience is primed and ready, the devices are numerous and increasingly sophisticated, and there are multiple content platforms to support the ecosystem. The last remaining piece of the puzzle is a robust ad economy, and by many indications this will be the year when it starts to scale."

Hear more of Verna's digital video insights in the latest episode of eMarketer's "Behind the Numbers" podcast:

These insights are drawn from eMarketer's latest report, "Digital Video Advertising Best Practices 2018: Connecting the Dots Across Screens and Formats." The report compiles best practices in digital video advertising from more than 20 industry experts who spoke with eMarketer, including executives at ad agencies, brand marketers, publishers, ad exchanges and tech firms. eMarketer PRO subscribers can access the full report here. Nonsubscribers can learn more here.