Backstory should be felt, not heard.
Let me give you an example of one of the finest authors to ever tell a backstory: Sir Arthur Conan Doyle.
I bet most of you haven't read Doyle. If you haven't read any Sherlock Holmes stories, do as I do, and with the movie coming out soon, take advantage of some of the re-prints of the Sherlock Holmes series.
In Sherlock Holmes, Dr Watson is constantly referring to outside cases, as well as his extensive list of notes on Holmes's cases. For example, here's the beginning of The Five Orange Pips:
When I glance over my notes and records of the Sherlock Holmes cases between the years '82 and '90, I am faced by so many which present strange and interesting features, that it is no easy matter to know which to choose and which to leave. Some, however, have already gained publicity through the papers...
And etc. See how he makes you feel the backstory, without telling it. Reading a little further along the same story, we see another volley of backstory:
Among my headings under this one twelve months, I find an account of the adventure of the Paradol Chamber, of the Amateur Mendicant Society, who held a luxurious club in the lower vault of a furniture warehouse, of the facts connected with the loss of the British barque Sophy Anderson, of the singular adventures of the Grice Patersons in the island of Uffa, and finally of the Camberwall poisoning case. In the latter, as may be remembered, Sherlock Holmes was able, by winding up the dead man's watch, to prove that it had been wound up two hours ago...
And again, etc. Do you see what Doyle did? Do you FEEL the backstory?
He didn't tell you all that happened. He didn't detail each case, nor did he dwell on any case in particular. Dr Doyle -- he was a doctor, like Dr Watson, who originally wrote his Holmes stories while waiting for patients to arrive -- touched his pen on the backstory of Holmes, building a huge and wonderful past for the detective and his loyal secretary, Dr Watson, all without ever telling the reader about the backstory.
JRR Tolkein did this in his series, constantly poking the reader with a backstory that was never fully revealed.
JK Rawlings does this with the Harry Potter series. Her backstory is a feather tickling the back of your neck, just below the brain stem, touching you in places so primal you don't even realize you're being backstoried.
You turn the page, feeling the history, unraveling the past, wrapped in a backstory you didn't even realize you'd read.
Remember these authors when you write. Let the reader feel the backstory. Don't cram it down their throat. Don't dwell on the backstory.
Yell, "ACTION!" Not, "BACKSTORY!"
Let it be felt, not heard.
Study Doyle. There's a reason Dr Doyle was knighted into Sir Doyle for his writing. It is because of his wonderful instinct for backstory that Holmes is one of the most beloved and well-developed characters in all of literature.
And he did it all without telling you a damned thing about Holmes! You just felt it.
See how that works?