Words like of, in, around, and from are prepositions. They are small words, but they can be very important! Mistakes with prepositions can make your ideas very hard to understand, and can even change the meaning completely.
Here are some mixed exercises: basic | intermediate | advanced (Ox)
under, around, at, on, towards
explanation (MyEnglishPages)
place exercises (Ox)
movement exercises (Ox)
no rules: you must learn each phrase
aware of, responsible for