try doing sets of chins for your first exercise on back day. i usually start out back day with pullups or chins myself, occasionally a row of some type, but its usually pullups.
set out to do 20 or 30 chinups, and get that many no matter how long it takes, even if your doing one per set at the end. when you can do 3 sets of 9-10 chins, change it to where your first set is pullups, then chins after that. you get the idea.
i used to do something like this, i went for 50 pullups/chinups in a session (when i started lifting i was one of those skinny guys who can do dips and pullups somewhat easily so fifty was doable).
and keep them on back day, dont do a whole bunch of extra throughout the week.
i think a lot of my back development came from my dedication to the pullup.
curse