As an iOS developer you’ve got the possibility to create promo codes using iTunes Connect. Each version of your app entitles you to 50 promotional codes which after given out to users can be used to get a free version of your app.
It only requires a few simple steps for a user to redeem a code:
Login to iTunes
Go to redeem page
Copy the code from the developer website/email to iTunes
Click the Redeem button
This is all fine, but there is a way as a developer to optimize this process:
An undocumented way of linking allows you to directly jump to the redeem page, with code filled in already. Use the following links on your website, in your email or in twitter posts to create the process of getting your app for free a bit simpler.
(via tap tap tap)