Chaturanga is generally only practiced as part of the so-called 'vinyasa,' or series of flowing postures which link one pose to the next: Chaturanga, Urdhva Mukha Svanasana (Upward Facing Dog), and Adho Mukha Svanasana (Downward Facing Dog). Because of this, there is an unfortunate tendency to flow through the pose rather quickly and neglect to refine the posture which robs Chaturanga of its strengthening benefits. Also, because we flow through Chaturanga so repeatedly in a vinyasa practice, poor alignment in this pose has the potential to lead to shoulder injury down the road.
Therefore, it is important to take some time in this posture to explore proper alignment and efficient use of our musculature to effectively align the shoulders and support the spine, not to mention build the power we need to flow through our vinyasas with grace and ease of breath. Keep the hands shoulder-width apart with the middle fingers parallel to one another and the elbows close to the sides. Draw the shoulders back and shine the heart forward. Do not bend the elbows further than 90 degrees and try to keep the forearms perpendicular to the mat, with the elbows stacked directly over the wrists. If the core muscles are weak, the hips will tend to sag to the floor, or we might overcompensate and poke the sitbones up to the sky. Use the bandhas to hold the belly firm and engage the glutes to counteract the tendency to tilt the pelvis forward. Active thighs will stabilize the entire body and bring lightness to the pose.
If you are working to build strength for arm balancing, inversions, and the like, I recommend spending at least 5 breaths in Chaturanga at least once per practice. Over time, add breaths until you can easily remain in Chaturanga for 10 deep ujjayi breaths without sacrificing the alignment of the pose. Remember your Chaturanga mantra: Strong belly, strong thighs.