[RonBee]

• "How often" adverbs expressing the frequency of an action are usually placed before the main verb but after auxiliary verbs (such as be, have, may, must):
  
  I often eat vegetarian food. (before the main verb)
  He never drinks milk. (before the main verb)
  You must always fasten your seat belt. (after the auxiliary must)
  She is never sea-sick.(after the auxiliary is)
  I have never forgotten my first kiss. (after the auxiliary have and before the main verb forgotten)
  
  Some other "how often" adverbs express the exact number of times an action happens and are usually placed at the end of the sentence:
  
  This magazine is published monthly.
  
  He visits his mother once a week.
  When a frequency adverb is placed at the end of a sentence it is much stronger.
  
  Compare:
  
  She regularly visits France.
  She visits France regularly.
  
  Adverbs that can be used in these two positions:
  
  frequently,
  generally,
  normally,
  occasionally,
  often,
  regularly,
  sometimes,
  usually
  http://www.edufind.com/english/grammar/ADVERBS5.cfm