The best way is the way that YOU can train at/near/above threshold for the longest intervals possible while leaving yourself at a fatigue that allows you to repeat the workout at appropriate intervals with sufficient recovery between and not burning you out from repetitiveness.
3x20's work, 2x20's work, 1x45's, 1x60s, 1x90s, 3-5x10's wth minimal recovery in between, STUCI workouts with correct recovery.
There is no secret to training threshold except to train threshold and recover, wash, rinse, repeat.
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