Align Deliverables with Strategic Business Objectives
I wrote the book, Manage Your Project Portfolio: Increase Your Capacity and Finish More Projects. That book is all about how you align projects with strategy, one project at a time.

Hint: It works best if you have incremental or agile approaches to your projects. And, having more interim milestones engage your sponsors. It's a win-win.
Determine Project Objectives
See the chapter about chartering your project in Manage It! Your Guide to Modern, Pragmatic Project Management.
Define Project Scope
I have used milestone and release criteria for years. (See more in "Manage It! Your Guide to Modern, Pragmatic Project Management") Release criteria explain the vital few criteria for release. You can use them throughout the project to manage scope.
Determine Project Constraints
There is no such thing as an iron triangle. It's much more of a pyramid. See Manage It! or Predicting the Unpredictable: Pragmatic Approaches to Estimating Project Schedule or Cost
Revise Project Plan
I have a ton of information about rolling wave planning and short deliverables. See Manage It! or Predicting the Unpredictable.