Don't underestimate the importance of a solid warm-up, especially when you lift heavier weights. Many people are guilty of foregoing a proper warm-up, which can sometimes result in rotator cuff injuries. Do a couple light sets of dumbbell front raises, lateral raises, and overhead press before jumping to the big weights.
Remember, you're up to 5 working sets. If you want to get through them all without injury, you need to prime your muscles!