[Thread]:
Steps for Improving Your Arabic Vocabulary
If you're still a beginner, then you need to go through book series like Bayna Yadayk.
For those who have a decent grasp of the language, study the following books in order:
1) Qisas al Nabiyīn by Abul Hasan al Nadwi
(1/5)

2) Suwar min Hayāt Al Sahabah by Abdul Rahman Ra'fat Basha
3) Al Nadharāt by Al Manfalūti
Now you should have a strong basis in the language, so you'd focus on expanding your vocabulary with less common words:
1) Al Muthallath by Qutrub
2) Al Fasīh by Tha'lab
(2/5)

3) Mukhtār Al Sihāh by Zayn al Dīn al Rāzi
4) Mufradāt Gharīb al Qur'an By Al Rāghib al Asfahāni
(This should really be read by everyone as it explains the meanings of words in the Qur'an)
5) Matāli' Al Anwār by Ibn Qurqūl.
In it he explained the uncommon words in
(3/5)

Al Muwatta' and Sahih Al Bukhari and Muslim.
6) Ikmāl al I'ilām by Ibn Malik.
This is similar to Muthallath Qutrub but longer.
7) Sharh Maqāmāt al Harīri by Al Shurīshi
As for poetry, the three most important books to focus on are:
1) Al Mu'allaqāt al 'Ashr and their shuruh

2) Al Hamāsah by Abu Tammām
3) Dīwan al Mutanabbī
A person who masters all of these books will become an expert in the Arabic language.
There are obviously many other books which I didn't mention, eg major encyclopedias and dictionaries like Tahdhib al Lugha, Al Sihah etc