Try to decide the size of the bird being observed. When you start looking in the guide books, the approximate size will be very helpful.
Smaller than a Sparrow – 2 to 5 inches
Sparrow Size – 5 to 8 inches
Robin Size – 8 to 12 inches
Pigeon Size – 12 to 16 inches
Crow Size – 16 to 24 inches
Goose Size – 24 to 36 inches
Larger than a Goose
Below are links to helpful articles on the internet about spotting birds and then how to identify them. There are plenty of online resources that specialize in this. No sense re-inventing the wheel.
Parts of a Bird from About Birds
Bird Idenification Tips from About Birds
Birding for Beginners Ten Tips for New Birders – from Wildbirds.com
There are some good articles on the internet that will help you get started identifying birds. Some of the simpler ones are:
How to identify a Bird – from Birdwatcher’s Digest
Bird Identification – from Wildbirds.com