stretch out your calves, hams, hips, quads and glutes a bit before the heavy squat sessions and a little inbetween but nothing drastic. Concentrate on powering through with your glutes and hips and lead with your chest. Keep your abs and lower back tight and push your elbows under the bar as you go down. Be explosive on your reps and dont fuck around laughing about while setting up, get in the "zone" for it and concentrate. That is the main reason I train alone cause otherwise I get distracted.