Answering the topic:
1 - Closer their ties with third-parties. Nintendo doesn't (actually, never) worked correctly with it's third-parties counterparts. Nintendo must change their philosophy that third-party games on their own system are direct competitors of it's first and second-party titles and a thread for them. Yes, that's the way Nintendo think and that's why third-parties are reluctant to work with. Nintendo should be more friendly toward them, just the way Sony and MS do. This'll bring more support and more sales.
2 - Expand their market. Nintendo is being conservative at best with it's franchises. Yes, they've created some new IPs, but very few were target toward it's old audience (not the casual which Nintendo is aiming). Wii Fit, Wii Sports, Wii Music, Nintendogs and Brain Training public is completely different from Mario, Zelda and Metroid one. It's been a long, long time that Nintendo don't announce a new big budget IP. They should do what Sony is doing investing on new big budget IPs (Uncharted, Resistance, inFamous, The Last Guardian etc). New IPs would expand Nintendo audience and attract new players as well.
3 - Invest on genres they never done before. I would love to see a sandbox, FPS, stealth, FF-like RPG and a realistic racer made from Nintendo first-parties. That would be a bold and different move.
4 - Less greed. Nintendo should make better use of their extense amounts of money instead of using cheap and simple strategies just aiming easy money (Animal Crossing DS copy and paste for Wii for example). Unlike many says, it wouldn't a bad idea for Nintendo to acquire more first and second-parties to work with. It worked with Sony and Microsoft, why Nintendo should miss the boat?
