Let's say that you receive a ciphertext and it is your job to decrypt it, you first need to find out which cipher it was encrypted with, then you can perform the appropriate cryptanalysis. First, I would analyze the frequencies of the letters in the ciphertext, if the frequencies seemed shifted, then you know it is a Caesar cipher, if the frequencies seem like normal English text then you know it was encrypted using a transposition cipher (we will talk about this). If it is not a caesar cipher or a transposition cipher, next take the Index of Coincidence of the text, if it is similar to English, it was encrypted using a monoalphabetic substitution cipher. Asa general rule, the lower the IC is the more complex the cipher used to encrypt it was. If it is not a Monoalphabetic Substitution cipher, try to decrypt it like we would normally do if it was a Vigenere cipher, if that does not work out, there is no general pattern to follow after that, just a bunch of hints.

To see if it is a Playfair cipher, split it into digraphs and see if there are any digraphs with the same letter repeated ("DD"), if there are none, it is a Playfair cipher.

For each next cipher I introduce, at the end of the post I will say the method that can be used to find out if a text was encrypted with that cipher