i do raw too, no boxes or anything, and i would definitly follow Nicks advice he knows what he is doing! but i have badish joints and like to really get warmed up by doing squats and leg curls
my squat warm up for squatting something like 455 in sets:
own body weight x 12
135 x 12
185 x 8
225 x 5
275 x 3
315 x 3
365 x 1
405 x 1
... then sets
when i powerlift style for something like 600:
135 x 12
225 x 6
315 x 3
365 x 1
405 x 1
455 x 4
500 x 3
550 x 2
... sets
also do some leg curl really light to get the knees warmed up
try alternating your footing a little, also make sure your right and left feet are equal distance from your midline. i had this problem left was always a couple inches out more and it made my squats really hard over time
finally, you should be sitting into a chair with weight distribution on your heels mostly but dont lift your toes or anything. put bar low on your back if you can (not too low), get out of the rack with knees bent... you probably know all this already but for others who maybe reading