Dirty woodstove glass? Try dipping a dampened piece of newsprint in the fine white ashes after your fire has died. Whipe it onto the glass in circular motions - it works well if the glass isn't terribly dirty to begin with.
Determine the daily oil consumption by dividing the number of days between deliveries to determine the average amount of gallons used per day. A sudden increase in the amount of fuel used daily could mean a fraudulent delivery took place or the burner is malfunctioning.