The link to the article has 3 but if your lazy here:
Good Habit No. 3:
Stretching
Upgrade to:
Stretching Between Sets
If you’re stretching at all, that’s better than nothing, and you’re already ahead of most lifters who give flexibility about as much attention as they do the new One Direction single. But it isn’t just insurance against injury or a way to avoid becoming restrictively muscle-bound. You can work some stretches into your training between sets to help you perform your lifts better and more safely. For example, the next time you deadlift, stretch your hip flexors during rest periods. Kneel on the floor in a lunge position and push your hips forward while contracting the glutes on your back leg. Hold for 30 seconds, then switch legs. Another option is to stretch your biceps between sets of curls, which can help them recover and be stronger on subsequent sets. Place your palm on a bench with fingers pointing back toward you, elbow straight, and stretch.