Side Plank pose (Vasisthasana) is excellent for strengthening the core, legs, hips, and shoulders.
Balancing on a block not only adds a layer of difficulty, but also creates a better alignment in the legs and hips.
Side Plank Pose with a Block: How to Do it Step-by-Step
Place your right hip on a block and your left forearm, palm facing up, on your mat. Align your elbow directly under the shoulder.
Engage your core to lift both legs to be parallel to the hips, squeezing them strongly together. Create one long line in the body.
Stay in this pose for 3-5 breaths, then repeat on the other side.