Something I wrote to a student of mine:
‘Arabic grammar on its own is not sufficient. You need to widen your reading to include: Arabic grammar, prose and poetry. I’ll give you list of some books I recommend on each below.
Sharh Shudhoor al-Dhahab by Ibn Hisham
Alfiyya ibn Malik with its various commentaries – I recommend the one by Ibn Aqeel and edited by Ahmad Shirbasy.