I used to read with one hand on my book and the other hand on a small paperback dictionary.
Make a guess using Latin roots and context before looking up. Put a little dot next to the word if you’re incorrect.
If you find yourself looking up a word that already has a dot next to it, take more care to take it in. Practice using it.
Or…if you’re not neurotic, maybe one of those word a day apps would help. :P