3 Weeks of "New" PRs
I know a group of elite hammer throwers who are so obsessed about setting new personal records every workout that they sometimes resort to inventing new drills on the spot, just so that anything they do with that drill will be a new PR.
Now as silly as that sounds, when you dig a little deeper, it's really not a bad idea for several reasons. If nothing else, hitting a new PR is uplifting. And it's also invigorating to do something new to break up the monotony. This jolt of enthusiasm tends to bleed over into the rest of your training as well.
Also, an important stimulus to hypertrophy is novelty. As a personal example, I did a few moderately heavy sets of trap bar deadlifts a few days ago (something I hadn't done in a long time), and I'm sore as hell from that, even though I've been doing conventional deads every week for years! Just that small change in body positioning was all it took.
The 3-Week Challenge
For three weeks, only perform exercises you've never done before.
You'll be quite surprised at what you'll learn about yourself. Most of us recognize the importance of shoring up our weaknesses, but not all of us are really sure what those weaknesses really are.
By instituting new exercises and methods into your training, you stand a better chance of accidentally discovering a weakness. It's like when you lose your car keys – the more places you look, the closer you are to finding them.