How to Work with the Four Levels of Transition in a Book: Smoothing the Reader's Ride

Successful transitions allow a reader to move through your book, from beginning to end, without getting frustrated or bored.  Or taking two steps back to reread something that wasn't clear.  But transitions are the last thing we think about when we're creating our books.  It's only when we read the manuscript at draft that we discover awkwardness, sections that jump around, or are too fast or slow.

How does a writer craft good transitions?