Present Simple or Present Continuous Tense?

What's the difference?

Present Simple	Present Continuous
Things which are always true: Water boils at 100 degrees.	Things which are happening at the moment of speaking: The water is boiling now, so you can put in the pasta.
Permanent situations (or nearly permanent; true for a few years at least): Julie lives in London.	Temporary situations: Julie is living in Paris for a few months (usually she lives in London). Situations which are slowly changing: I'm getting better and better at speaking English.
Habits or things we do regularly: I drink coffee every morning.	Temporary or new habits: I'm drinking too much coffee these days because I'm so busy at work. Annoying habits (usually with 'always'): My flatmate is always leaving the kitchen in a mess!
Future events which are part of a timetable: My plane leaves at eight tonight. To talk about the future after certain words ('when' 'until' 'after' 'before' 'as soon as'): I'll call you when I get home.	Definite future plans: I'm meeting John after class today.
To talk about what happens in books, plays and films: At the end of the book, the detective catches the killer.	To talk about people in pictures and photos: In this photo, my mother is walking beside a lake.

Remember:

We use the present simple with stative verbs. We can't use any continuous tense (including the present continuous tense, of course) with stative verbs.