The Prophet said, “Do the prostration properly and do not put your fore-arms flat with elbows touching the ground like a dog. And if you want to spit, do not spit in front, nor to the right, for the person in prayer is speaking in private to his Lord.”
Clear words: “do not put your fore-arms flat with elbows touching the ground like a dog“.
Distinguish your sajdah from the way a dog lays down on the ground, physically and in meaning.
Read relevant Hadith here.