It seems some lifters think they are going to curl the bar. If you begin the lift with bent arms, the first moment of the pull goes to straightening out your arms, wasting valuable drive where you need it most. Now a bit on lifting gear. Conventional deadlifters should try to use slipper type shoes or wrestling shoes. They fulfill the rules for footwear and are low to the ground, thus further decreasing the distance the bar must travel.
Some lifters deadlift with work boots or high heeled squat shoes.
These are a no-no for deadlifting as they increase the distance the bar must travel and position you more forward over the bar, causing you to pull back as well as up as I discussed earlier. Sumo lifters might try a flat soled cross-training shoe as they may need more foot support because of the wide stance used. Lastly, I have found that certain squat suits help greatly in the deadlift. I myself gained about 40-50 pounds by using a specific squat suit. Some squat suits are terrible for the deadlift, but some that were worthless for the squat prove to be effective for the deadlift.