It should not be nearly as hard to play with my friends on a Nintendo system as it currently is. Friend codes were never a good idea, and this is the perfect opportunity to improve on the competition with a robust suite of online options. Nintendo has a fantastic community, but with how difficult it is to communicate let alone play with one another, this is the most obvious change that needs to happen.
*Drop the "Creator's Program"*
Another no-brainer, this has been bad policy from the beginning. More than ever before, games can live and die by its exposure to the watchers, and subsequently the creators, of content on YouTube and Twitch. A game that is played by a major personality has an almost guaranteed increase in sales, and at the bare minimum will get increased search traffic from the likes of Google.
The restrictions in place are more than slightly frustrating for many creators, and while some have embraced the "Creator's Program", it is more of a begrudging acceptance than it is a successful and popular program. Sony and Microsoft do not have any kind of similar program, and no major publisher does either. Nintendo needs to get with the times on this one, or continue to see its smaller titles struggle to find any kind of audience.
*Work with 3rd party publishers*
Nintendo has an awful track record with many publishers, including EA, Ubisoft and Activision, who make up the majority of commercially successful titles. Part of this is due to the multiplayer being so restrictive, but many companies have gone on record that it is difficult to work with Nintendo to port titles or even create exclusive titles. Nintendo has some of the most iconic, highest rated and commercially successful titles in video games, but that isn't enough to keep a system afloat, as evidenced by the WiiU.
Despite being out a year before PS4 or the Xbox One, the WiiU has a frankly abysmal library outside of the games published by Nintendo, and 10 excellent titles isn't enough to keep anyone except the most hardcore of Nintendo fans. If the NX is going to be a success, it is going to need major hits, and not just once or twice a year with Nintendo developed/published titles.
*Drop the gimmicks*
The Wii and the WiiU were both consoles that had an interesting concept, but at the cost of actual hardware to support AAA developed games, resulting in mediocre graphics and mechanical limitations. Both "motion" and "second screen" were and are still interesting mechanical features, Nintendo can no longer rely on neat gimmicks if they want to capture any of the core gaming audience. Nintendo President Tatsumi Kimishima has said that the NX is not going to be "the next version of Wii or Wii U."
*Don't forget your roots*
For a long time, Nintendo was synonymous with innovation and creativity. A new generation console is a good time to bring some new, and fresh ideas to the well established franchises. But this does not mean that Nintendo should abandon what has worked so well for them. I'm sure there will be a new Mario RPG, as well as Mario Kart, and probably a new, exclusive Legend of Zelda title. If anyone can combine new ideas within already established franchises, it's Nintendo, so while many things need to change, it is also important that not everything does.