There is a lot to learn about when we use present continuous and present simple.
I would thoroughly recommend any student of English to buy the book:
English Grammar in Use (Intermediate) - by Raymond Murphy - Cambridge University Press.
The first few chapters deal with exactly this issue. There is a step by step explanation and lots of exercises to do afterwards. There is also a key to the exercises at the back of the book. I think you need to go into this area of study in some depth.
- For Teachers