We prefer the Present Perfect Simple for permanent situations or for longer time periods:
I've lived in Ahmedabad for six years, (this is my permanent home) I've worked for this company for ten years, (it's my permanent job)
We prefer the Present Perfect Continuous for temporary situations or for shorter time periods:
I've been living in Delhi for six months, (but my usual home is in Ahmedabad]
I've been working here for a month, [a comparatively short time]
But it is often possible to use either the Present Perfect Continuous (to put emphasis on the length of time) or the Present Perfect Simple.
I've been teaching English for twenty years, or I've taught English for twenty years.
In ‘How long have you been watching TV?’ we are interested in the continuous length of time; but in ‘How many programmes have you watched today?’ we are interested in the number or amount.
We often use the Present Perfect Continuous if we are interested in the activity. Perhaps it is completed or not:
She's in the bedroom. She's been sleeping for twelve hours.
We use the Present Perfect Simple if we want to emphasize that the action is complete, finished:
She is ready to work. She has slept well, (she's not sleeping now)
Here is another example:
We use the Present Perfect Simple (Not the Continuous):
- with already, ever, never, still, yet: I haven't written the letter yet.
- with verbs which cannot be used in continuous tenses like know, forget, notice:
I've known her for a year, (see Unit 93.)
- to talk about short sudden actions:
I've broken the window. She's had an accident.
-to talk about the last time we did something:
I haven't eaten meat since 1998.
