Just read…read a lot. Read a wide variety of genre…fiction, non-fiction, historical fiction, etc.
The library is your friend…and is free,
Honestly, I can’t see any reason why a student would need to “study” this during the summer to get a leg up. Read…read…and read some more.
If writing is an issue, maybe find a creative writing course…but really…why are you concerned about getting a leg up??