In K.M. Weiland’s book Outlining Your Novel she covers this well.  The book is great in a lot of areas but regarding backstory I picked up these gems:

• We must give our characters backstory.
• Sometimes the most effective backstories are those that are hinted at rather than told outright.
• No lengthy flashback scenes…present backstory with a powerful punch and few words.

In addition… backstory may be better off staying inside your head.  It may do the reader more benefit to have you use the backstory in order to drop into a fast paced read at just the right moment.

Do yourself a favor and read her book, especially if you have trouble with the outlining process…. and do your future self a favor by knowing ahead of time where this beast you’re creating is heading.

Onward,

J