Chaturanga is part of the sun salutation series and can also be a great way to build strength when practiced by itself. The pose requires a lot of strength to perform correctly, so modifications are a great idea until enough strength is developed to be able to hold the pose with relative ease.
From Plank, keep your legs firm and the tailbone tucked and firm the shoulder blades by engaging the seratus anterior muscles (the muscles on the sides of the rib cage). Keeping weight evenly distributed across the hands, lower down until the torso is a few inches above the floor. If the belly drops and the lower back curve deepens as you lower, try dropping to the knees before lowering to maintain focus on keeping the core steady. The legs should be slightly rotated inward and the toes still tucked under, and energy moving back out the heels.
As you lower, make sure that the elbows hug the sides of the waist. Letting them wander away from the body means you are relying too much on the pectoralis muscles instead of building up strength in the shoulders and arms. For most beginners, the shoulders will stay above the elbows and the forearms will have a slight backward angle. Eventually, you can come slightly forward so the forearms are perpendicular to the floor and the elbows higher than the shoulders. This requires quite a bit more strength. It also means that when flowing into upward dog, you need a really deep backbend in order to keep the shoulders above the wrists and get the full benefit of that pose, so find the modified version until you have sufficient openness and strength developed.
A good way to practice the specifics of the pose is to come up against the wall and practice upright, standing a few inches away from the wall with the hands a little lower than the shoulders. This way, you can practice keeping the proper alignment without having to hold your entire weight.
If you have any questions, please leave a comment below. I’d love to hear from you or see you at one of my classes!