Bakemonogatari
Start here; it defines the style and cast.
Watch order
Monogatari Series
A release-order route for one of anime's most famous nonlinear supernatural franchises.
Nisemonogatari
Continue release order.
Nekomonogatari Black
Short prequel before Second Season.
Monogatari Series Second Season
Major character arcs.
Kizumonogatari I-III
Origin story; release order places it here for impact.
Owarimonogatari
Late-series core material.
Zoku Owarimonogatari
Epilogue-style continuation.