Short Tutorial - How to break codes when you have little to no clues
Writing out the actual alphabet helps, as you can see when letter shifts, or when something is inverted (first example), or can see it in number terms
look for unnatural repeats in letters
look for repetitions, they can sometime mean something, repetition can sometime be used to hide other words in its very existence
numbers can be used in a number of ways, but they usually have a reference to somewhere in the line, or to each other
Hope this helps xD
(will add to top)
Edit: Added hints to the 3 codes