Making a bike go faster involves two factors: weight and aerodynamics. There are many ways to reduce the weight of the bicycle (not the least of which is to reduce the weight of the rider — improving rider fitness is the best way to make a bike go faster.) There are also a number of ways to improve the aerodynamics of the bicycle. This article will address a few of the most cost efficient ways of reducing weight and improving aerodynamics. It will not address improving rider fitness.
A bike's wheels are the single most important piece of equipment in terms of increasing the speed of the bike. You want wheels that are strong enough for the type of riding that you will be doing, but as light as possible.
The second piece of making your bike more aerodynamic is adding components that make it easier for you to ride in an aerodynamic position. The first item to consider would be aero-bars. These are bars and/or pads that can be clipped on to your handlebars and allow you to lean forward, placing your forearms on the handlebars, and bringing your body lower toward the frame. Although riding in this aero position will not be comfortable for the entire ride, it will help you go faster, especially into the wind.