At 40 km/h, 83% of your effort is used to overcome aerodynamic drag, so reducing aerodynamic drag is the key to going fast on the bike.
1. The Win Tunnel - great series of videos from the Specialized wind tunnel - for faster for the same effort
2. Water bottles - the aerodynamics of different water bottles and placements
3. Aero hacks - GCN goes to the Boardman Performance Centre to compare the effect on aerodynamics of ride position, rain jacket, etc, on a road bike. You can even learn the best way to pin your race number!
4. Ways to improve aerodynamics - good blog article by amateur time trial racer