Ask around and you find the same habit everywhere: meet a new word, look up the Vietnamese, write it down, and feel like progress has been made.
Then it is known today and gone tomorrow. And when you need to say something, you freeze, with no idea how to fit the word into a sentence.
The MFPA frame
Look at every new word from four angles.
Meaning. Not just the translation, but what the word actually does. For example, the is used when both speaker and listener already know which thing is being referred to.
Form. What does it combine with, where does it sit in the sentence, does it change shape.
Pronunciation. Look it up properly. The has two pronunciations: /ðə/ before a consonant (the book) and /ði/ before a vowel (the apple).
Appropriateness. Where does this word belong, formal or familiar. Using something in the wrong register causes more misunderstanding than a grammar mistake does.
How to use it
If you are studying alone, slow down the next time you meet a new word. Draw four branches, M, F, P and A, and fill them in.
Go slow at the learning stage so you are not endlessly revising it later. That is the whole idea.