Your vocabulary is one of the first ways that someone you have just met will judge you.  If all that you can do is refer to some object as a "thingy," then there is a strong possibility that others, well . . . may think you are not that bright.  On the other hand, if you try to dazzle people by your command of language by using "big" words in which you are not quite sure of the meaning, you very well may make a fool of yourself.

With out a doubt, the best way to increase and refine your vocabulary is to read.  Read lots, read often, and read from varied sources.  It's good for your vocabulary.  It's good for your mind.

Below is a list of words that I think are good to know.  They are words that I consider to be useful, interesting, or entertainingly odd.  You may never use them, you may never hear or read them, but if you look over the list, you will at least have come across them.  There is no rhyme nor reason to the order, but I have clumped together words that have something in common.

Tectonic
Zeitgeist - the spirit of the time; the taste and outlook characteristic of a period or generation.
Incongruous
 
Innocuous
Noxious
 
Archetype
Amorphous
Biannual
Biennial

Ontological
Epistemology
Cosmology
Phylogeny

 
Scatology
Feces
 
Behoove
Prolific
 
Copious
Plethora
Multitude
Multitude
Ubiquitous
 
Esoteric
Contingent

Continously
Continually
Constant

Contruct
 Fruition

Demagog - an orator who appeals to the passions and prejudices of his audience.
Obfuscate - to make so confused or opaque as to be difficult to perceive or understand.
Hegemony - the predominant influence, as of a state, region, or group, over another or others.

Erudite
Loquacious

. . . more to be added . . .