Before Development

There are a few some things to consider before designing or developing your app.

First get to know the platform in general

http://channel9.msdn.com/Events/Build/2014/2-509

if you want to review some basics there are also some C# questions often asked.

http://www.microsoftvirtualacademy.com/training-courses/twenty-c-questions-explained

Design:

You need to design your app before developing. When thinking about designing your app you need to think about three main things. Color, Iconography, and font. 

https://kuler.adobe.com/

http://www.flaticon.com/

http://www.fontsquirrel.com/

Design for developers:

http://bit.ly/DesforDev

Develop:

Now it is time to develop and know what APIs you can play with. With 8.1 Development there are 2 things to keep in mind, your XAML and your Code-Behind.

Code:

http://www.microsoftvirtualacademy.com/training-courses/building-apps-for-windows-phone-8-1-jump-start  (This is the most important link on this page. It takes you from A to Z )

https://onedrive.live.com/?cid=635551367e71f947&id=635551367E71F947%219356&ithint=folder,.pdf&authkey=!AOeQrnexu96M3O8

XAML:

http://channel9.msdn.com/Events/Build/2014/2-516

http://channel9.msdn.com/Events/Build/2014/3-591

Store:

Now you have to publish your app. Go to the link below and create an account and your app should be published in a few hours. YES, unless there is something absolutely wrong with your app it will pass certification in a few hours.

http://dev.windowsphone.com