Windows Phone 8 App Development: A Quick Start Guide
Windows Phone 8 app development is made easy with free Windows Phone SDK 8.0 provided by Microsoft. Developers can download SDK and start to create Windows Phone 8 apps that can work on software emulator that comes with Windows Phone SDK. After registering for Windows Phone Developer account, programmers can register their Windows Phone 8 physical devices to test and validate their apps on real smartphone devices.
In this guide, I tried to list required steps and give short information about tools and software to create Windows Phone 8 apps. You will also find reference links and tutorials for more detail about these tools. Software developers who want to build apps for Windows Phone 8 can find details I have tried to summarize in this development guide at Windows Phone Dev Center
Requirements
If you want to develop a Windows Phone 8 app, you require a 64-bit Windows 8 Pro or a higher operating system. Windows Phone 8 apps development can not be done on a Windows 7, Windows Server 2008 or on a Windows Server 2012 computer. You need a X64 Windows 8 PC cor Windows Phone 8 app development.
For the Windows Phone Emulator which enables the Windows Phone developer to test build applications requires specific requirements.
You can find details of those hardware, software and configuration requirements at given reference 
App development using software and tools included in Windows Phone SDK 8.0
Software & Tools
If you have Microsoft Visual Studio 2012 Professional or higher (Visual Studio Ultimate or Visual Studio 2012 Premium editions), the development tools and project templates are integrated with the Visual Studio installation.
If you do not have Visual Studio 2012 Professional, you need to download Windows Phone SDK 8.0 (Windows Phone Software Development Kit SDK 8.0) using download link
You can further read tutorial Download Windows Phone SDK 8 for Visual Studio 2012 and Windows Phone Emulator and see how you can download Windows Phone SDK 8.0 and install it with step by step screenshots.
Besides setup screens, you can also find how to turn on Windows 8 Hyper-V Platform feature to avoid Windows Phone Emulator configuration errors.
Windows Phone 8 SDK includes all required tools to create Windows Phone 8 apps.
Those tools required to create a Windows Phone 8 app can be listed as follows:
Microsoft Visual Studio Express 2012 for Windows Phone,
Project templates used to create new Windows Phone apps, and
Windows Phone 8 Emulator for testing and debugging your app on a software emulating a Windows Phone 8 device.
Besides Visual Studio Professional, Premium or Ultimate editions, Blend for Visual Studio can also be used as a design tool for your Windows Phone 8 app. Isolated Storage Explorer command line tool (ISETool.exe) that comes with Windows Phone SDK or Windows Phone Power Tools can be used to browse, upload or download files from IsolatedStorage of your Windows 8 phone.
Simulation Dashboard for Windows Phone can be used to test your application under heavy network traffic cases or under similar real word scenarios.
Windows Phone Application Analysis is an other software tool for app monitoring and profiling your Windows Phone app to provide a high performance and quality product.
An other important tool for app developers for Windows 8 phones is Windows Phone Store Test Kit.
This test tool is also known as Marketplace Test Kit.
Windows Phone Store Test Kit provides a prevision and shows possible problems with your app when you submit your app to Marketplace for the first time.
So developers can detect and work on found issues to correct them and submit their apps without any problem an saves time in submission process.
Sign up for a Developer account
In order to test your Windows Phone 8 app on a real Windows Phone physical device as a second step after testing it on Windows Phone 8 Emulator, you need to sign up for a developer account and register your Windows Phone 8 phone. This developer account costs $99 USD per year.
First you should have an active developer account on Windows Phone Dev Center. You can follow the registration URL for details and benefits you will get when you sign up for the developer account. Then you can register your phone using Windows Phone Developer Registration tool with your developer account.
You can find details for registering your smartphone for testing your Windows Phone 8 apps, please refer to
Create your first Windows Phone 8 app
Before you start to develop your first Windows Phone 8 app, I strongly suggest you to read what is new in Windows Phone SDK 8 to learn updated features and new features introduced with SDK 8.0
There is a great article about new and updated features in Windows Phone SDK 8.0 at
If you are ready, you can start creating your first Windows Phone app
Create your first Windows Phone 8 app
After you setup your Windows Phone 8 app development environment, you can start working on Windows Phone samples provided by the Windows Phone SDK team.
You will find a large number of sample applications that you can download and study over them for your future Windows Phone apps.
You can download sample applications following given reference