MS needs to focus on improving the quality of the apps on the platform. Major apps such as Facebook, Twitter, Instagram, Vine, Yelp, Flipboard ect. While they are all present on the platform many are severely lacking in quality compared to their iOS/Android counterparts and have not seen updates to them in months. I know there are 3rd party alternatives that work great and are well liked by the hardcore fans, but in order for MS to actually succeed and gain any significant market and mind share the official apps need to be well supported and be at feature parity with their other OS counterparts.
Its the quality of apps that will help to lure new users to WP and as of now the quality just hasn't been there enough on WP and therefore users have no reason to choose it given that they can get a better, more complete experience on other platforms.
The actual biggest problem I think WP has to deal with is the lack of quality and feature parity of apps with iOS/Android. I think people who actually use the phone and try the interface by in large really enjoy it. It has hands down the best user experience interface of the three major platforms, but the official apps lag behind in features and support.
If the apps kept up with the improvements made to them on iOS/Android it would be so much easier to get people to be investment in the hardware and software ecosystem. MS can't keep trumpeting the fact that it has cool official apps for WP if they are rarely updated and have less features and speed than their counterparts.
Realistically what can MS do to combat this problem? What is their long term vision for this platform?