Here is a useful quote from Zinsser's "On writing well", a timeless guide to all such matters:

> Keep your paragraphs short. Writing is visual—it catches the eye
> before it has a chance to catch the brain. Short paragraphs put air
> around what you write and make it look inviting, whereas a long chunk
> of type can discourage a reader from even starting to read.
> 
> But don't go berserk. A succession of tiny paragraphs is as annoying
> as a paragraph that's too long. I'm thinking of all those midget
> paragraphs—verbless wonders—written by modern journalists trying to
> make their articles quick 'n' easy. Actually they make the reader's
> job harder by chopping up a natural train of thought.