Chaturanga From Top to Toe
Many people have a hard time learning how to roll over their toes in the transition from Chaturanga (Four-Limbed Staff Pose) to Urdhva Mukha Svanasana (Upward-Facing Dog). It can be challenging to develop this ability, but it is worth the effort, as it will encourage you to use your legs in a way that will strengthen your Chaturanga and will help you to end up in a correctly aligned Upward-Facing Dog, in which your lower back is protected and stabilized by the action in your legs.
The important thing to understand is that the action in the feet actually originates in your legs. To develop this technique, start in Plank Pose and engage your quadriceps so that your legs are very actively involved. Maintain this intention as you lower into Chaturanga, and pause, sternum extending forward, lower belly gently lifted, tailbone down, quadriceps firm. With your chest still reaching forward, use the strength of your legs to press back through your toes so that they in fact travel back slightly on your mat as you roll over onto the tops of your feet. Just after you begin this action with your legs and feet, pull your sternum forward and up, drawing yourself into Upward-Facing Dog. Make sure that, as you do this, you have firmly anchored the tops of your feet onto the mat so that they don't travel forward with your chest. In your Upward-Facing Dog, stack your shoulders directly over your wrists. The proportion of "push back" through the toes to "pull forward" with the chest is different for everybody, and you will have to tinker with this a bit to find out exactly what works for you. Your aim is that, with your sternum and thighs actively lifting, your shoulders will be exactly over your wrists.
What's terrific about mastering this transition is that it really forces you to use your legs in poses where they sometimes get left out. Strong, active legs will facilitate your Chaturanga, drive the roll-over/slide-back to Upward-Facing Dog, and protect your backbend once you get there by preventing you from over-bending in your lumbar spine.