The last message was encrypted using an affine cipher, 'a' to 'q', 'b' to 'z', 'c' to 'i', i.e. moving on nine letters each time. The problem with just using one cipher to encrypt all the letters in a message is that we maintain the frequency of letters in the plaintext, so we're able to use frequency analysis to help decipher it. We could instead use different alphabets for different parts of a message. For example we could encrypt the odd letters with one cipher and the even letters with another. This is called a Vigenere cipher with keyword length two. Good luck!
abcdefghijklmnopqrstuvwxyz KEYWORDABCFGHIJLMNPQSTUVXZ