I've talked in depth about the problem with Windows Phones before, such as the lack of apps or variety of OEM's. I'm really not in the mood to write three paragraphs of information so long story short...
Nokia must release a true flagship phone that competes directly with the best Android and Apple devices both on paper and in real life. This means the latest technology, in every aspect. Not because the phone needs it(since Windows tends to be more efficient) but because it impresses the normal man.
Work on polishing the platform to make it look nice and be more functional. Make it faster, make it even more personalized.
Once OEM's such as HTC and Sony see how far Microsoft has gone, and a phone that can compete with the best they have, they may see the logic in jumping onto the Windows Phone train. And instead of making a Windows Phone has a side project, as OEM's have done before, they may truly focus on making a good, powerful Windows Phone that gives people more variety. And people who previously were big fans of HTC or Sony would now consider Windows Phones, since HTC or Sony would have one released.
OEM's supporting you, you gain the support of app developers. Developers previously forgetful and often lazy when it comes to Windows Phones would update and create apps to support the rising platform supported by major Android names. Local businesses and companies would start creating apps for Windows because on a business level Microsoft tends to be the best way to go and since everyone uses Microsoft computers and tablets in a business(unless it's iPads) the ability to sync with your phone would be greatly appreciated.
Okay that was a lot longer than I intended I apologize. And it still doesn't quite portray what I'm trying to get at. If you don't agree give me feedback, not insults, haha. I'd appreciate a good argument that isn't someone telling me why Android or iOS is better, like most forums, haha. Thank you.