We talkin bout Practice......
"It's always been my worst lift, and no matter what I do it doesn't seem to increase"
This will always be true if you truly believe that.
So many amazing lifters train in so many different ways, but the one thing that unites them is self belief and mental drive.
However, if you feel you have lots of mental drive and are simply stalling; I recommend more benching, heavier benching and benching more often. But, in particular....
Week 1: 60 lifts @ 80% of 1RM
Week 2: 40 lifts @ 85% of 1RM
Week 3: 20 lifts @ 90% of 1RM
Week 4: 10 lifts @ 95% of 1RM
Week 5: 20 lifts @ 65% of 1RM (speed/deload)
Week 6: New pb.
Do this however you want. Sets, reps, days are all irrelevant as long as you achieve with good form. Your strength and neural development is dictated by overall tonnage and average intensity. Hypertrophy is more biased to what reps/sets were achieved, but building muscle as a drug free lifter can be like pissing in the wind dependent on genetics and fiber types. Getting strong is more like improving your Call of Duty killstreak; it's a skill and not a physical attribute... the brain learns to recruit more fibers and have stronger contractions once the golgi tendon dampens through practice alongside improvements in rate coding.....it's all mental aspects.
People are always shocked when the answer is do more of what you want to get good at....
Anyway, your technique is fine looking at the video. Take or leave my advice, but I will eat my squat shoes if you follow that to the letter and not hit a pb providing you are eating and sleeping enough.