1. Look for short words first; there are only two one-letter words in English, and there are only a handful of two-letter words (brainstorm with your friends -- what are they?). Each word in English must have a vowel in it, so if you can figure out the two-letter words, you will probably have found several vowels!

  2. Look for doubled letters. Frequent doubles are the pairs 'ss', 'll', 'oo', 'ee', 'nn', 'pp'. Hardly ever in English do you see 'aa' or 'yy', and 'uu' (unless the message happens to be about vacuums!)

  3. A more advanced technique is called frequency analysis, which is used to break ANY simple substitution cipher. To use this, count the occurrences of each of the letters in the ciphertext (e.g., 17 X's, 12B's, 9 C's, 7 P's, etc.). Then look at a standard English frequency table and guess the identity of the letters based on the table. In pretty much any English text, the nine most frequent letters will be E, T, A, I, O, N, S, R, and H, with E leading the pack (usually by a lot).

    Along with looking at the frequencies of letters, it is often helpful to consider how letters relate to one another. You can often tell which ones are vowels because vowels are "friendly," that is, most letters appear before and/or after them. Thus, if there is a letter in your ciphertext that appears in pairs with many different letters, it may be a vowel. To find out which one it is, remember that 'a' is almost never doubled, 'e' is incredibly frequent, and 'u' is relatively rare.

    Another helpful trick is to consider digraphs, that is, pairs of letters. The digraphs also follow frequency patterns, so finding out which of your digraphs is most frequent will often reveal information about your ciphertext (see the digraph frequency table). To count the digraphs, it's helpful to make a 26x26 table, with all of the letters labeling each row and column. Then, if you see the pair "VQ", put a hash mark in the space on row "V" column "Q". Obviously, this takes some work, but if you work as a team it can be done quickly!

  4. The letter 'q' is unique in English in that it is always only followed by a 'u'. Assuming you have a long enough piece of ciphertext, if you see a letter in your ciphertext that is always only followed by a letter you suspect is a vowel (e.g., if every time you see the letter 'V' in your ciphertext, it is always followed by a 'P', and you already think that 'P' is a vowel, you can guess that 'V'='q' and 'P'='u'.