Type of Being
How cool that "type of being" can be a tool of characterization. When you have a novel with so many types of races, though, there will certainly be distinctions among them. The Elves are all tall and fair and learned and graceful. The Dwarves all have long beards and love metal and rocks. Hobbits are short, usually fat, and generally merry. The Black Riders are wraiths: formless, shadowy, and terrifying. Men get a little trickier. As in the real world, some are good and some are bad. But their very ambiguity is like another character trait: as a type of being in Tolkien's world, men are harder to pin down at first glance than Elves, Dwarves, or of course, Orcs. Still, in general, if you are looking at a Dwarf in The Fellowship of the Ring, you already know that he probably does not love Elves, and that he lives in the mountains. If you are looking at an Elf, he probably loves forests and singing a lot. It simplifies matters a lot to be able to fit each character into a category right off the bat, thanks to his or her (or its!) type of being.
Generally, when a character is tall and fair in the Lord of the Rings, that's a good sign. One of our favorite descriptions of Frodo is that, for a Hobbit, he is "taller than some and fairer than most" (1.10.39). Being tall and fair is one of the (many) ways we know Frodo is marked by Destiny. Furthermore, if you can manage to shine with light, that's also a mark in your favor. When Frodo is busy passing out on the far side of the Ford of Bruinen, he sees a shining shape fighting the Black Riders: it is Glorfindel, the Elf-lord, whose power shows itself as white light. By contrast, the Black Riders are terrifying in part because they always appear shrouded in shadow. And the Orcs are a misshapen and grotesque lot – clearly evil, even at first glance.
Of course, while physical appearance does indicate something about moral value in this series, you can't always judge a book by its cover. For example, Aragorn's first meeting with the Hobbits does not inspire them with his greatness. But Aragorn is deliberately trying to keep his long lineage and kingly destiny hidden from the public eye. When Frodo sees Aragorn in Rivendell, he appears grave and learned, a far cry from the scruffy vagabond he first met in Bree. Aragorn has the ability to lie low and appear less than what he is, thus using appearances to influence opinion.
Speech and Dialogue
This one is pretty obvious. It's no mystery that Sam Gamgee, a working-class Hobbit who acts as Frodo's servant, talks in a rougher and more casual manner than Elrond, half-Elven Lord of Rivendell. Tolkien conveys a lot about a character's social standing and personality strictly through dialogue. For example, we know that Barliman Butterbur is a bit of a fool because he tells Frodo about his letter from Gandalf: "And I'm mortal afraid of what Gandalf will say, if harm comes of it. But I didn't keep it back a-purpose, I put it by safe" (1.10.48). Tolkien gives us something of the flavor of Butterbur's accent ("a-purpose" instead of "on purpose"). His concern about "what Gandalf will say," rather than the damage that might have been done by not sending this letter, indicates that Butterbur is not in on Gandalf's counsels, nor does he understand the importance of Gandalf's business. Butterbur is a perfectly nice guy, sure, but his dialogue indicates to us that he is not one of the Wise.