As you may know, the "ing" or "ng" sound is one of the most controversial sounds for a non-native English speaker. Not just for Iranians, for most people it's hard to pronunce it correctly. Actually it's not that much hard, most of the learners just don't know how to pronunce it. I have seen many advanced learners who pronounce it wrong. They say "ing", such as in reading, sing or singing, hang or hanging, wrong, amazing, boring and so on. This pronunciation is completely wrong. It is a nasal sound at the end which is articulated with the back of the tongue, there is no "g" at the end. You never hear a native speaker saying "ing", they say "iŋ". We can also pronounce it as "in" or "ən", very short version of "in". For example somethin, or somethən. British people pronounce it "in", and Americans usually say "iŋ". So we don't say writing, going, something, anything, building, boring, sing or singing, hang or hanging, wrong, tongue, song. Instead we should say writiŋ or writin, goiŋ or goin, somethiŋ or somethin, anythiŋ or anythin, buildiŋ or buildin, boriŋ or borin, siŋ, siŋiŋ or siŋin, haŋ, haŋiŋ haŋin, wroŋ, toŋ, soŋ.
I have prepared some sentences with which you can practice the "ŋ" sound. I hope it will be useful for you. First I read the wrong version of the sentence, then I read it in the right way so you could pay attention to their differences.
1a. She is watching a boring movie.*
1b. She is watchiŋ a boriŋ movie.
2a. I am reading an interesting story.*
2b. I am readiŋ an interestiŋ story.
3a. They are living in an amazing building.*
3b. They are liviŋ in an amaziŋ buildiŋ.
4a. I am enjoying being here.*
4b. I am enjoyiŋ beiŋ here.
5a. Will you sing a song at the spring fling? *
5b. Will you siŋ a soŋ at the spriŋ fling?
6a. The king wore a large signet ring on his finger.*
6b. The kiŋ wore a large signet riŋ on his finger.
7a. You are wearing too much bling for the wedding.*
7b. You are weariŋ too much bliŋ for the weddiŋ.
8a. I like to play ping pong.*
8b. I like to play piŋ poŋ.
9a. There is one thing I’d like to know.*
9b. There is one thiŋ I’d like to know.
10a. The king likes to sing in the evening.*
10b. The kiŋ likes to siŋ in the eveniŋ.
P. S. * indicates the wrong pronunciation.
“ŋ” is the IPA symbol for “ng” sound.