The Hub

Brom

First of all, you need to ask yourself how relevant the backstory is to the current action. If there is an aspect of it which is vital for readers to know (i.e they can't infer past events from what is happening in the story at that moment), then put some in but keep the bits short (no longer than a sentence or two at a time). Parcel out the info throughout the scene. Again with complex thoughts and feelings, those can be conveyed (shown) through actions, body language, internal dialogue and dialogue with other characters and again, those can be interspersed with any expository action in the scene. The object is to keep the story moving forwards and not halt it in mid-flow with long passages of information which bore readers and make them skip those bits.