Learning words and how to use them is much more important, though roots will also help.
I'd suggest making flashcards. On the front of the card, write the word and an easy pronunciation.
For example, PRODIGAL prah-dig-ul
On the back, a brief definition, a mnemonic, a short sentence using the word in a memorable way, and a couple of synonyms, found on m-w.com.
For example:
PRODIGAL: wasteful
PRADA GAL
The PRODIGAL PRADA GAL spent $1200 on a pair of boots.
Synonyms: spendthrift, profligate
Making cards like this will help learn words as opposed to just memorizing them.