The bird dog is a simple but effective glute and hip stability exercise that’s especially useful in training preparation.
Position yourself on hands and knees and keep your entire trunk tight with a neutral spine. Simultaneously lift and reach one arm and the opposite side leg up and forward/backward. Aim to reach at least horizontal with both, but you can also maximize the range of motion you have. It’s a good practice to add an isometric hold of the final rep of each set for 5-10 seconds.
The bird dog strengthens the glutes and helps stabilize the hips and the entire trunk, in particular against rotation.
Bird dogs should generally be done for sets of 10-20 reps/side. They make a good addition to training warm-ups.