for, Benefactive: the entity that benefits form the action.
to, Goal: the entity towards which the activity is directed.
A. It's very important for students to study English every day.
Students will benefit if they study English.
B. It's important for doctors to know that what patients need.
Doctors will benefit if they know what patients need.
C. It's important to me that he reads my novels.
That he reads my novels is important to me (the goal)
D. It's important for me that he reads my novels.
I will benefit from his reading my novels.
All the best, :D