If you are playing for a living or just trying to make a decent consistent profit this is a must. Read it, learn it, memorize it. Roy Cooke has long been my favorite gambling author and he makes great points in a short article here about how to approach bankroll. Focused on poker, but the theories of stepping down and what you need to step up can be easily applied to sports betting.
http://www.cardplayer.com/poker_magazine/archives/showarticle.php?a_id=14754
http://www.cardplayer.com/poker_magazine/archives/showarticle.php?a_id=14754