I don't stretch, as such, before a workout. I simply start my squats with just the bar for a set of ten and then then do another set with a couple of 5Kg plates for another ten.
I use these two sets to limber up and feel for any kinks, occasionally hold the hole for a few moments. I'll then take another set of five with one plate at each end and usually I'm then warmed up and ready to start ramping the weight.