This post covers the less frequently-encountered races: Half-elves, Dragonborn, and Half-orcs.

Half-Elves

Half-elves are those elves with significant human bloodlines or humans with significant elven blood. Sometimes they are exactly 50-50 mixes, but that's much rarer. 

Unlike the more common races which have distinct phenotypic subgroups, half-elves are a continuum and exhibit significant variation between members of the race. Half-elves with high elf backgrounds tend to be taller than humans with blonde or gem-colored hair. Half-elves with wood elf backgrounds tend to be shorter than humans (but not by much) with darker hair and skin. Half-elves in general have less physical sexual dimorphism than humans. Females tend to have slightly more pointed ears, but that's about it. Half-elves grow more facial hair than elves, but less than humans or dwarves. Physically, half-elves are found with the looks of either of their parent races.

Human-dominant Half-elf society (Earth-kin)

Although there is little physical polymorphism within the half-elf race, there a significant divide in social attitudes. Those half-elves who take after human-kind rigidly adhere to the meritocratic ideals of human society. In essence, they try to be more human than the humans. This group tends to marry humans wherever possible. They are accepted generally by humans, but rejected strongly by pure elves of both types and are called "mutaverta" (mud-bloods).

Wood-elf dominant Half-elf society (Travellers)

Those half-elves that take after the wood elves are wanderers and travelling merchants and traders. The closest earthly parallel are the Romani (gypsy) people, although the half-elves will settle for short periods of time (until too many people move in). These are the half-elves that most frequently marry other half-elves.Their social standing has improved tremendously in the Council Lands in recent years.

Byssia--almost all half-elves in Byssia (and there are a lot of them) are wood-elf dominant. They are just as settled as any other Byssian, however, and are culturally indistinguishable from the human or elven populations (depending on who they live among. 

High-elf dominant Half-elf society (Sharp-ears)

The smallest group are those that take after the high elves. They prize arcane ability and try to marry into elf families. The high-elves look at them as second-class citizens but cherry-pick the best to be adopted into the families. Humans detest them as wannabes and accuse them of putting on airs. They are very rare outside the capital.

Stone Throne--the half-elves (a large minority of the population) are descended from high elves. Many of them consider this to be a social status marker.

Dragonborn

The dragonborn are the last remnants of a race of magically-engineered super-soldier race dating back to 800 BC (before cataclysm). Most of the dragonborn race were killed at the final battle of the Cataclysm War, fighting for the civilized world. Since the rediscovery of The Remnant Dynasty 5 years ago, the majority of the dragonborn have coalesced in that kingdom and been accepted into their clans.

Dragonborn have different elemental affinities (colors) that are randomly expressed. There is no strong genetic tendency for one color over another.

Female dragonborn tend to be larger (5'10-6'2", 190-250 lbs) than males (5'2"-5'10", 150-200 lbs), but males are more aggressive.

Half-orcs

The half-orc people are a race of pariahs and outcasts. They are mostly human with less than 50% orc blood, but the orc blood frequently dominates. Sometimes "clean" parents give birth to children with noticeable orcish features (tusks, green skin, etc). This results in the whole family being dropped from their posts and exiled to the north. A few males are employed as guards in the capital, but otherwise they are very rare and are despised and hated by all. This antagonism is lesser to the north where they are more common.

Physically, males are significantly larger than females. Males average 6'2" and 230 lbs while females average 5'6" and 160 lbs. Males also have more pronounced tusks and tend to be bald on the tops of their heads. Females tend to strongly express their secondary sexual characteristics. While males are only very rarely fully human-looking, it is not uncommon for a female half-orc to "pass" as human (although with a slightly different skin tone).

Emotionally, males are prone to blind rages especially when they are intoxicated. Females are much quieter and maintain the society. Reading and writing are considered female practices--males rarely learn more than the basics. Tribes are ruled ostensibly by a chief, but the wise woman (tribal shaman) is really in charge in all matters except war. Inter-tribal relationships tend to be peaceful.

Arcane magic is rare; half-orc casters tend to the clerical or druidic (and female). The few arcanists tend to be elementally-oriented.