When deadlifting, think about putting force into the ground – keep your toes down. This works better than just thinking about lifting the weight or leaning back.
Lifters need to learn the "tripod" foot, which means the foot has three points of contact with the ground. That larger base of support is essential for creating a rigid foot through which you can put force into the ground.
Lifters and athletes have traditionally been taught to drive through the heel, and this isn't necessarily incorrect. But as a result, many athletes will go to an "elf slippers" set-up where their toes lift up.
ELF SLIPPER SETUP
This creates a lean-back approach to deadlifting more than a true force production scenario. You'll often see lifters fall backward after setting the weight down because this is a false positioning of the center of mass. You may even see the knees wind up behind the heels during the lowering phase, especially on stiff-leg deadlifts.
So get your feet firmly rooted to the ground and deliver force through them.