Linking verbs -- am/is/are/was/were -- drain a prose of urgency and force a certain amount of distance between the reader and the action.
When used sparingly, a carefully chosen 'was' can add a subtle magnitude to your prose. When overused, it can make your prose feel dry and bland.
Whenever possible, swap out linking verbs for stronger, more active verbs. For example: "She was standing on the pier" becomes "She stood on the pier", and so forth.
Source: http://jwtroemner.wordpress.com/2013/04/10/diy-editing-was-and-other-has-beens/