I wrote about how to write a great pull request on my blog
Link to ticket
This is always helpful as a way to connect the different methods of communication that your company uses within your Product Development teams.
Description of Ticket
A description of the ticket, explaining potential changes in the code or away from the original intent of the story
This may be a synthesis of offline discussions you had surrounding the code you wrote. It could include what decisions were made, or realizations come to surrounding necessary codebase changes.
Why you made these changes
I like think of this from a users perspective. This could look like a User Story
"A User should be able to do X"
Again this creates further clarification around the purpose for this pull request, which can result in stronger suggestions from those reviewing your code. Potentially even highlighting miscommunication or stimulating debate around what the original ticket was supposed to mean.
How you made these changes
How you went about changing this functionality
This could be said to be redundant due to your great git history but including it here prevents some simple context switching between the git history and your PR documentation.
High, Medium, Low
Risk involved with this pull request. Are you changing the primary login or payment gateway? Well let's make sure this doesn't blow up