1.) Use a coat hanger (or motion pro P/N 080368 ~$20) that you straighten out to measure the distance between the Axle Nut and the Swing Arm Pivot on each side of the bike to make sure the wheel is in the bike straight.

2.) Use the Harley-Davidson Belt Tension tool, Part Number 40006-85 about $28.

You can usually "get away" with using the twist method, but some bikes (like mine) have to be done absolutely by the book.