This is a cryptogram puzzle.
In English language, the one letter words are: I and A.
So if you see a symbol in the code that is just one symbol forming word - chances are it is I or A.
As mj2c mentioned - in words that are made up of several symbols; the more often the symbols are found might be deduced that they are vowels (a, e, i, o or u). Then you deduce if that is so or try them and see if a word is formed.
Then if a 2 similar symbols are side by side; they might be those letters that are commonly seen in English words: tt, ll, oo...