I'm very keen to learn Arabic Grammar because I have holidays now (free time )
The benefit of learning Arabic grammer is that you'll be able to properly understand Quran when you recite the words inshallah and you'll appreciate it more. I'm planning to watch a series of lectures on the Medina Arabic book. The course is very popular and a lot of people apparently say that it has really improved their Arabic. The teacher is amazing judging from the lesson I watched.
This is an excellent book series for anyone wishing to come out speaking Arabic (or Modern Standard and Classical Arabic) with a high intermediate proficiency. I do prefer the newer edition of the book in 7 (short) books rather than 3 (long) books plus supplementary materials (answer keys), it was a lot more difficult for a student studying on his own and the new edition is better if you're on your own: https://archive.org/details/DrV.AbdurRahim.MadinahArabicReader