Chaturanga dandasana is a tough nut to crack. In its ideal form, the pose hovers above the floor, the body perfectly straight, the arms strengthened by their 90 degree angle. Getting to this position takes time and arm strength, which you gain by doing more and more chaturangas. Know when to say when, however; if your arms and shoulders start to feel fatigued and you are losing the integrity of the pose, switch over to knees, chest, and chin for the rest of class.

This pose has been a challenge for me! From laying prone on the floor and using it to lift into plank and then dog – I can get to about where the model is, but pushing all the way up into straight arms has been too much.
Is there any magic trick, or just keep trying?
The pose is more often arrived at the other way around, coming down from a plank position, and that is definitely the easier way to go. To build arm strength, I like to practice coming from chaturanga back into plank instead of rolling forward to upward dog. Again, it just takes time to build the arm muscles to do this. An added plus is that it really tones the triceps and biceps.