When a plateau sets in (and it always does), most people freak out and start a complete overhaul of their training or diet without getting to the bottom of the issue: the body's adaptation to what was thrown at it. That's what the body does. It adapts to stress and even dietary practices. You have to give it a reason to move past that set point. But don't go nuts!
Reduce carbs or fats by a small margin for a week or two and measure progress. Don't overhaul your entire diet if it worked for weeks or even months on end.
Deload for a few days if you feel drained. If you've done several workouts without progress, don't overhaul it. Make minor changes to create something new for the body to adapt to. It can be as simple as changing the rep range, moving foot or hand or bar position, or adding in a new intensity technique. From there, you'll be able to gauge how well this addition worked for you. If it doesn't work, make another small change.
Don't panic when you hit a strength, size, or leanness plateau. Make small adjustments to smart, proven programs rather than starting over from square one with something else.