Word Order : Position of The Adverb

always, usually, sometimes, often, never, ever, still, also, almost, already, probably, seldom, definitely, hardly ever, occasionally, ...all & both

I. The adverb goes before the verb:

I usually smoke 20 cigarettes a day.
Does Ryan always arrive on time?
We hardly ever saw each other when we were at college.
Russell and Lauren both like diving.


II. The adverb goes between the auxiliary and the verb:

I have never been to Island.
People don't always know what they are doing.
They were all concentrating hard.
You will never change.
Sara can play the piano and she can also play the flute.


III. The adverb goes after am/are/is/was/were:

This train is normally on time.
I am always tired in the morning.
David was still there when I arrived.


NOTE:
probably goes before the contracted negative:

I probably won't be able to attend class tomorrow.
I will probably not be able to attend class tomorrow.

Source : Grammar Tutorial