The German "ng" in "Hunger", "singen" or "Wange" is pretty similar to the "ng" in "walking", it's represented by /ŋ/ in the IPA. I.e. it's more of a nasal /n/, the "g" almost disappears. If the "g" is preceded and followed by a vowel as in "Liege", it's the same as at the beginning of a word ("Glocke"), i.e. the same as the English /g/ in "get", unless the word ends in "en" ("legen", "liegen", "lagen"), then many (if not most) Germans don't pronounce the last syllable as /gən/, but instead turn it into a nasal /gn/, dropping the e/schwa altogether. If a word ends with a "g" as in "Weg" (path), it turns into a /k/ sound (but you probably know that already). Hope that helps!

German is not my first language, but as far as I am aware there are no 'rules' for this. Take a word like 'gegangen' it has two games in the middle ( ignore the first letter for this explanation). There is very little difference between the pronunciation of the first g and the second. The second g might sound a little different because of the n in front of it, and the first a little different syllabic emphasis on the first g.