Adverbs of frequency (from higher to lower frequency) :
always- usually-often-sometimes-hardly ever/seldom/rarely-never
Position: between the subject and the verb (I usually get up at 9 a.m), after the auxiliary (I have never travelled to China) or after the verb to be (I am never late). Sometimes can also be placed at the beginning and at the end of the sentence.
Expressions of frequency:
once/twice a month/a week/a year (once= one time)
Position: at the end of the sentence (I go to school every day).
There some other time expressions which can also be used to express frequency (e.g, on Mondays/weekdays, in summer/April/the morning, at night/noon, etc.).
Here’s an exercise to practise.