Education on pricing labor

We seem to continually overprice bids.  I think it comes down to hours DLHs and fringe hours we calculate.  Is there any recommended reading or training on how to calculate labor and DLHs and fully burdened rates?  For example, if the government wants a T&M rate for a certain 19 week period, an annualized rate calculation doesnt potentially recoup all the costs, if the person uses some of the time off in the period.  What is the best practices to determine the denominator of DLH (productive hours)?  This type of training and guidance would be helpful.