The most advanced and effective method for improving deadlift strength and mechanics is performing eccentric isometrics on squat-stance deadlifts. This method is also highly potent for stimulating full body hypertrophy as the intensity of contractions in the lengthened position, combined with constant tension and occluded stretch, make this a difficult combination to beat.
Furthermore, the eccentric isometric allows you to fine-tune your body position and movement mechanics as emphasizing the stretch promotes increased sensory feedback from muscle spindles and other proprioceptive mechanisms.
Start off by using 50-70% of your 1RM and progress from there. You'll also want to elevate yourself several inches by using a box or plates in order to allow for full range of motion in the stretched position. Focus on lowering your body slowly during the eccentric while feeling for optimal positioning. This will help you find the natural stopping point at the bottom.
Then hold this position for several seconds to reinforce these ideal mechanics into your central nervous system. As long as you don't collapse, the range of motion should only be 1-3 inches below what you would typically go to when touching the floor. The goal is a natural but not excessive range of motion.