How does someone train using 了 correctly? I'm really bad at 了ing: Nankai students say I'm bad at this.  My teacher says I'm bad at this.  Even Tang Ho mentioned my abuse of 了.  Moreover, I'm sure I'm not the only one who is really bad at 了ing: e.g. To 了 or not to 了.

Question: How does someone train using 了 correctly?

To make this clear...

Not relevant: Where does 了 goes in one particular sentence.
Relevant: Where does the 了 go in these 100 training sentences?

I.e., training, drills, repetition, etc.  Keep doing it until I get it right without thinking.  Maybe there's an app or book that gives you where does the 了 go? exercises.  Or maybe there's a way to generate my own exercises.



Example

To illustrate why this is so difficult...

(Note: putting 了s in the following example sentence does not answer the question---that's not the point!  That's "give a man a fish" not "teach a man to fish".).

In theory... I've read about completion 了 (post-verb) and change-of-state 了 (end of sentence).  Aside from 太...了 which is easy, that covers most 了s (as I understand).  I'm aware there's a lot of other cases I have no idea about yet.

In practice... I'll want to say something very simple like:


  I gave my friend a phone call
  我给朋友打个电话 [without any 了s]


So I think:


the phone call is complete, so it needs a completion 了 (but do I put it after the verb 给 or after the verb 打?); and
at some point, the state changed from

(1) me having not given my friend a phone call, to
(2) me having given my friend a phone call,

so it also needs a change-of-state 了.


At this point I'll give up and copy/paste the sentence into Baidu 我给朋友打个电话 and just copy what someone else has done.  In this case, it seems like no 了 is needed, despite me thinking there's a reasonable argument for adding three different 了s.




   But there's one sound mode that no one knows...
   What Where does the fox say 了 go?
It is a tough question I would give it a try...

了
(1) [aspect marker] indicating completed action
(2) [final particle] indicating change of situation

Let's use a shorter sentence.

I go to see the flower (我去看花)


If you want to state the verb 去 (go) is complete, the sentence would be (我去了看花)

If you want to state the verb 看 (see) is complete, the sentence would be &quot;我看了花&quot; (I've seen the flower)

if you want to indicate the verb phrase 去看花 (go to see flower) are completed action the sentence would be &quot;我去看花了&quot; (I've gone to see the flower).

if you want to indicate the situation has changed, the sentence would also be &quot;我去看花了&quot;. You would say that if the context is Q: &quot;去看花沒? A: &quot;我去看花了&quot; (situation changed from 'haven't gone to see the flower' to 'have gone to see flower')

if you want to emphasize the action &quot;去看花&quot; then sentence would again, be  &quot;我去看花了&quot;. You would say that if the context is : &quot;老闆，工作做完(現在)我去看花了&quot; (Hey, boss, the job is done, I am going to see the flower now)


我去看花了 can has three different meanings in different context, deciding where to put 了 in a sentence without other context is not easy indeed.
Conclusion:
To use 了 correctly, you have to:

Identify which action is completed and which situation has changed, just think about what your sentence would be like in English, and you will find some clues.

Consider what you want to express by filling in context in your mind, like in my &quot;我去看花&quot; example.