Race fit jersey and shorts... anything baggy is just extra drag
Aero helmet like the giro synthe, s-works evade, lg course, etc
If you can't stay in the drops then stay as low as you can on the hoods
Shave your legs... seriously.. specialized tested it and it makes a difference
Check the wind forecast before heading out for your ride... adjust route accordingly.
Clean up the cabling on your bike, if you have long shift and brake cables try to route them closer to your handlebars and frame... cables... while small are surprisingly unaero.
Better tires, Continental GP4000s are aero and have low rolling resistance.
and... don't put your head down even on a trail, that's just asking for trouble.