Using what we already know about the data to decrypt it?
I recommend you will read a bit about chosen-plaintext attack.
If the scheme you are using is CPA-Secure then even when an adversary is choosing two different plaintexts, giving them to the challenger and then the challenger picks one of them, encrypts it and sends it back to the adversary - the adversary won't have an efficient algorithm to find out which one was encrypted.

AES-CBC with random IV is assumed to be CPA-Secure if my memory don't betray me. So, If you are using the encryption right, the knowledge of the structure of the plaintext should not help you.