There are generally five major things to consider when trying to identify birds.

1. Size & Shape are more beneficial to note then field marks in narrowing to type of bird.

2. Overall color pattern is a key to using a field guide after you have determined the type of bird it may be. An understanding of individual variation in birds and season to season changes can help identification.

3. Behavior tells a lot about the type of bird and an experienced birder can sometimes identify a species just by watching how it flies, eats, or flicks its tail.

4. Habitat is where a bird is found foraging, nesting, or roosting. The type of habitat can change based on the need, but generally you find a Nuttall's Woodpecker in oak and riparian woodlands and the very similar looking Ladder-backed Woodpecker in Mojave desert vegetation.

5. Distribution and range, birds are atypical from land based creatures being that they fly but for the most part they are found in a restricted area depending on the time of year. For example an American Pipit breeds in alpine vegetation and northern latitudes but winter in the valleys and lower latitudes. So while you wouldn't expect to see this bird in the summer in the Kern River Valley, it is common here in winter. Knowing its normal range and distribution helps to narrow the focus to more common species for your area. As the saying goes, if you hear hoof beats assume horses not zebras (unless you are in Africa!)

Size & Shape

field marks not as important
group or family bird belongs to
size and shape
compare body parts

recognize family member by height build at a distance

practice on common birds
tiny
small
medium
large 
huge

compare to other birds that you might know 
size
hummingbird
sparrow
robin
crow
hawk
duck

Impression
thin
fat
chunky

Shapes - big/small long/short
head
tail
bill
wings

Compare birds to each other
length of bill compared to head