Vocabulary Study

Memorizing lists of words is one way to learn vocabulary, but it is just about the least effective.  The most effective is to read, a lot, starting when you are about 3 and continuing throughout your life.  But that doesn't serve your purposes in the present.  

The best way you can approach learning vocabulary later in life is to study the ways words are composed; that is, you should study common roots, prefixes, and suffixes.  These are the building blocks of words.  While studying a list of 100 words might net you 100 new words in your vocabulary (assuming you do not forget them shortly after you study them), studying just 25 roots or prefixes might net you several hundred new words just by knowing the core elements of those words.  

Here is a quizlet someone made to help students study such vocabulary building blocks.  There are several others as well as numerous websites and programs dedicated to this simple approach to the lexicon.  Consider a simple practice of learning a root or prefix/suffix each day and see if that doesn't help your understanding of difficult texts.