Exhale - Drop to your knees, chest, and chin. Keep your butt high and your elbows hugging your ribs.
If you are more advanced:
Exhale - Shift your weight forward a few inches and lower down to chaturanga dandasana. Bringing the shoulders slightly in front of the wrists before lowering helps you get the alignment right in the final pose. If you are getting tired, opt for knees, chest, chin since doing chaturanga incorrectly can injure your shoulders over time. (See 5 Most Dangerous Yoga Poses For Beginners for more info.)