There are a variety of standard processes. Refer to PMBOK or Mulcahy sections on Closing a project. They have good stuff. The biggest risk that plagues most troubled projects at the end is lack of "field readiness", meaning the product is ready to deliver and the customer environment isn't groomed to incorporate it into their operations. Many strategies to fix that. Also, time really should be taken to journal a retrospective, or "lessons learned". This is a great final roundtable worksession with the teams. There are others too.
Many do indeed vary from project to project, but these are more typically in the product management rather than the project management. Product management is where you find Lean, SixSigma, etc. These practices have unique wrap-up processes, beneath the project management layer. You need to look to the methods for the wrap-up tips.
My guess is you'd find a good start to your question by referencing Mulcahy's PMP Exam prep book. Not a lot there on the topic but what is there is pretty good.