Although if the OP is in the 16'ish mph range for average speed
3) Using the drops more often
then staying in the drops more will save energy that can be used to ride faster speeds for more of the ride. Therefore having a better average speed than sitting up. But maybe not as much of an increase as the OP wishes.
When doing 20 mph or more, One should be able tell a big difference in more aero in the drops as opposed to less aero. Pedaling is much less effort to hold a particular speed.