Study the human skeleton in an anatomy book. You will need to be familiar with not only the size and shape of each bone, but also the location of each bone in relation to others and its purpose.
Note the salient features of the bone. Bones like the cranium, mandible, and scapula will be fairly obvious because of their distinct shapes, but metacarpals and phalanges (bones of the hand) may not be. A femur may be identified by its robust size, but a radius may be difficult to distinguish from an ulna on first glance.
Examine the ends of the bone. If you can't identify the bone based on its shape and size, the ends of the bone may point you in the right direction. For example, the radius and the ulna are generally the same shape and size, but the ulna has a hook-like surface on one end, whereas the radius has an expanded end with a wider surface.
Search for minute characteristics that distinguish between similar bones. For some bones, you might be able to identify its type based on shape and size (e.g., vertebrae, metacarpals), but not which specific bone it is. In that case, you will need to examine it for small attributes. For example to identify a specific vertebra, look for small openings (foramen) in the parts that project sideways from the vertebral body (transverse processes) or flat spots (facets) on the body's sides. Minute characteristics can also help you identify metacarpals, phalanges, and other bones that require further scrutiny. Your anatomy book should give you a list of these characteristics for each bone.