200 English Grammar Mistakes!: A workbook of Common Grammar and Punctuation Errors with Examples, Exercises and Solutions So You Never Make Them Again

Too-short paragraphs:
 Some students are fond of writing two to
three sentences in a paragraph. A paragraph should be detailed and
concise about the central idea you are conveying.
Multiple  ideas:
  A  paragraph  should  only  explain  one  particular
line of thought or idea. You should avoid cramming several ideas
into one paragraph.
Poor  structure: 
Poor  structure  in  writing  a  paragraph  can  be
related  to  the  arrangement  or  focus  of  the  paragraphs.  Every
paragraph  should  have  a  focus.  It  is  better  to  start  with  a  topic
sentence first before writing the subordinate sentences.