How to deduce an unfamiliar word and increase my vocabulary?

I highly recommend getting yourself an etymological dictionary. Etymology is the study of the origin and history of words. Every word you find interesting or you find unfamiliar, look up the meaning and then check out its origins. Becoming familiar with the foundations of the English language will help you to figure out the meanings of new words by pulling them apart and identifying the separate building blocks. That will include suffixes and prefixes, but most importantly the roots - useful when many words share the same basic root. If you don't have it already, you may develop a love for language as a whole, not just English.