Know if it is fixed or correctable
Assess the amount of osteophytes
Release MCL around to semimembranous
Assess PCL if using CR
Consider downsizing tibial and removing additional medial bone
Further Reading:
Master Techniques Knee Arthroplasty - Lotke and Lonner
Chapter 7 by Scuderi and Insall
Advanced Reconstruction of the Knee AAOS
Chapter 27 - Varus Knee - Windsor and Choi
JAAOS Article Dr. Mihalko - http://upload.orthobullets.com/journalclub/free_pdf/19948701_19948701.pdf