Once you're familiar with a word, then you can deploy it like a weapon. That means that not only do you understand its meaning, but you also know its synonyms and understand its meaning within its context.
Synonyms: A synonym is a word that is similar in meaning to another word. For example, "large" is a synonym of "huge," and vice versa. In the Word Knowledge section of the ASVAB, you'll be presented with a list of words, and asked to pick the word that most accurately matches the word you're given in the question - in other words, the synonym. When you learn a word, be sure to learn a few synonyms for it.
Tip: Remember, a synonym matches the word type. So a verb ("run") would have another verb as a synonym ("sprint"), and a noun ("delight") would have another noun as a synonym ("happiness").
Context: Mastering the ability to learn words and understand how to use them will help you out on sentence comprehension. Often, if we come across a word we don't understand, we figure out its meaning by looking at the context (the sentence or paragraph surrounding the word). For example, look at this sentence:
I'm not sanguine about our chances, but I'm prepared to take the mission anyway.
You might not know what the word "sanguine" means, but you can guess from the rest of the sentence that it means "optimistic" or "enthusiastic."
General Study Tips: Military.com has put together a no-muss, no-fuss list of study tips that should help you no matter what you're studying for.