Find out all the important words/phrases in the book and examine how the author is using them. Figure out what they mean with relation to how the author uses them.
The most important words/phrases to focus on are the ones that give you trouble. Likely these are important to the author as well. Even if he has important words that don’t bother you, chances are you have understood them.
One way of finding the important words: Does the author place any stress upon certain words and not others?
Another way: Does the author quarrel with other writers on the meaning/use of the word?
Once you have discovered the important words, what next? Either the author uses these words in a single sense or he uses the same word in multiple ways. So find out if the word has one or several meanings. If it changes meaning, look at the context for clues on the meaning.
A good book is like a jigsaw puzzle. A good book has parts that all fit together. But most books are not good, and the author may jump around with the meanings capriciously. Don’t waste too much time figuring out the meanings of words here.
A term is not a word or set of words. It is more like a concept. The author may use different words for the same term!