One quick way to get stronger is to activate more muscle. An easy way to do that is to grip hard.
Squeeze the bar, grab the ground. For any exercise with a bar or handle, squeeze it as if you want to leave finger-sized dents in the bar. On the ground, grab the floor, turf, dirt, or pavement.
When you squeeze a bar, or when you grab the ground like you were going to tear up chunks of turf, you activate your hand muscle. And your forearms. And your upper arms. And your shoulders.
Try it. Make a fist and put your other hand on your forearm. Squeeze the fist hard - feel the muscle in the forearm contract?
This has two basic effects: you recruit more muscle (making the movement stronger) and you make yourself more stable and stiff (making the movement easier.) The first puts more muscle into the move, the second makes it more like pushing on a broomstick instead of pushing on a rope.
You can do this with your feet, too - grab the floor or the inside of your shoes with your toes. Then, without letting your feet actually rotate, attempt to turn your right foot clockwise and your left counterclockwise. Twist them into the ground as if you were screwing them in. You'll generate more torque and more tension.
Don't open your hands. No matter what you are doing for a lift, don't relax your grip at the top or bottom. Don't open you hands at the top of your biceps curls - you're relaxing your biceps, too, and missing out on some time under tension. Don't open your hands with a press overhead - you are losing some stability. Open your hands when the exercise is over, not during it!
This will make you instantly stronger in a movement. It also has the nice effect of making you better at the movement. And if you are stronger and better in a movement, you can load it more, or do more reps, or otherwise progress with it. That leads to more strength, more muscle, and more effective movement.