What most naturally follows?

How to frame a doorway
Choose a door.
Since doors come in so many different dimensions, you'll first have to decide the type of door you want to install. Most doors are going to be 30 " or 32 " wide and 80 " tall; however, this is far from universal.
Choosing a door will allow you to make all of the proper measurements for the doorway. If you haven't decided on an exact style of door, at least decide on an exact size, so you can get started on the doorway.