Considerations
According to Birds.com, there are nine factors to consider when identifying birds: size, color, shape, bill size and color, leg length and color, eye color, flight pattern, habitat and distribution. Comparing a bird's song with a description or recording is another option.
Body Parts
Before you can consult any reference book or online source about which bird you have spotted, it is helpful to know the parts of a bird. Noting specific features of the bird's head, body and wings can make identifying a bird easier.
Drawing a Sketch
It is helpful to draw a sketch when you spot a new bird. Make notes of the bird's coloring and any other distinctive features. It might be helpful to start with a generic bird sketch and add coloring and marking notes to the sketch. This will help you remember while the bird is in sight to note details about all areas of the bird's body.
Using a Field Guide
Field guides such as "Audubon's Birds of America," the "National Geographic Field Guide to the Birds of North America" or the "Stokes Field Guide to Birds" can help in identification. A good field guide will have various and detailed photos of birds, along with good descriptions and may even include notes about threats to the bird's habitat.
Consulting a Poster
The weekend birder may wish to consult a poster such as the Project FeederWatch's Common Feeder Birds available online. The free poster comes in several different versions to cover many different types of domestic birds, and comparing what you see or your drawing to the poster can help determine which bird you've heard.