Mastering spelling rules or spelling patterns, that is, peculiar yet fairly regular ways English spelling works. This includes patterns such as the 'hard c or g' vs. 'soft c or g' rule (the reason these expressions are in single quotes is that these are not technically sound terms):
When followed by 'e', 'i', or 'y', 'c' and 'g' have their 'soft' sound (that is, /s/ and the 'j' sound), but when followed by 'a', 'o', or 'u' they have their 'hard' sound (/k/, /g/). This alternation can be seen in the words gym, gin, and gentle vs. game, go, gum; and cent, city, cyst vs. cot, camera, cup. There is a relatively large number of such patterns in English spelling.