I can think of no greater contributor to reader confusion than the preposition.  Use too many of them and you've asked the reader to make too many connections (when one is all they want to make). 

Here’s one more rule on prepositions – don’t end the sentence with one. 

It has the effect of making the sentence trail off. A preposition makes a connection between two things and if nothing appears after the preposition, it is considered an incomplete thought.