What I am Lacking

I have no corrections. Personally, I would have said "Part of my job" or "One part of my job" rather than "A part of my job," but that is just a personal stylistic preference.

If you want to build your vocabulary there are several ways to do so. You could look at the reference section of a major book dealer and find a book on vocabulary development. You could also check out exam preparation guides. These often contain word lists of the so-called big words as you call them. Be careful about using unfamiliar words! You may be misusing them. You may even come off sounding a bit stilted if use the $50 words in conversation.

Two useful guides are Funk and Wagnall's Guide to Synonyms and Webster's Guide to Synonyms.These are probably available at a University library. They contain chunks of word groups and explain subtle nuances and shades of distinction between the synonyms. An especially useful feature is that these guides contain sample sentences using the words.

If you re unsure whether you are using a word correctly, consult the Oxford English Dictionary. The OED has sentences for each word.

Another way to improve your vocabulary is to read some of the great political theorists of the nineteenth century. John Stuart Mill's "On Liberty" uses words with eh utmost precision.

I was in much the same boat when I took the (old) SAT at age 11. I didn't know many of the vocabulary words so I needed to memorize word lists. By the time I took my GRE, three years later, I did not need to study from word lists; I knew the vocabulary already from my studies. If you read widely enough, you will not need to study from word lists. But they are a good way to get started.