principle which is considered to learn language

Some general principle which is considered to learn language :
First principle
Knowing language means being able to
To read it
To write it
To speak it
To understand it when someone spoken
Second
There are two kind in language use :
Receptive language activates:
listening and reading .
Productive language activates :
speaking and writing .
Third
Enough (input)
we should make enough input before ask for production even if we do a lot of mistake.
above are three principle it must considered in learning language .