With Windows Phone 8.1 developer preview right around the corner, we are all very excited to get our hands on this. Also, it is not fair that only developers get it so there is an easy process we can walk you through on how to get this app.
Step 1: Go to App studio and register
Step 2: You go through a few easy steps signing into your Microsoft account
Step 3: Download the app Preview for Developers for Windows Phone
Step 5: Read the directions and press next
Step 6: Read the Terms and Conditions (if you really want to) and accept
Next, check the Enable Preview for Developers and click done
All you have to do is check the phone update and install when a new update is available. I had the preview on my Lumia 822 and used it to get GDR3 early. It worked very well and did not negatively affect my Lumia 822.