"Learn just fifty essential word parts (roots, prefixes, and suffixes) and you will unlock the meaning of over 100,000 words."
Akash, the key to learning vocabulary is ROOTS, ROOTS, ROOTS! I can not stress this enough. Learning word lists is next to useless. Learning vocabulary by topics is, in my opinion, not much different. But learning roots is exciting, fun, eye-opening, and EXPONENTIAL!
If you understand the component parts of words, you will unlock their meaning. An understanding of roots is probably one of the most powerful tools you can have for learning and remembering English vocabulary. Roots will give you a deeper understanding of known words, they will provide help in learning new words faster, and because roots reappear continually they will help you remember words with ease because you will, in fact, not be 'remembering' at all - instead you will be thinking logically. If you are in a technical/scientific profession, roots are an absolute must. Think about it, Akash: more than 70% of all English words come from Latin/Greek roots; the figure jumps to 95% if we are talking about English words with more than one syllable.
I am in the process of transferring my very popular 'Roots' course online. It will take another two or three months to complete the process. My primary aim for this course is not only to teach the meaning of roots, but also to set them firmly in your long-term memory. Most importantly, I want students to have fun studying roots.
My course will aim to teach approximately 100 word roots over a six month period (this has yet to be defined). It is well worth studying these 100 word roots because they provide a solid foundation to all future vocabulary learning. After the course, students will be able to speak concisely and with precision, they will understand better, and they will be able to understand unknown words at a glance. Needless to say, the course will provide a good vocabulary foundation for GRE, Toefl, Ielts etc. Remember: "an impressive vocabulary makes an impression."
I'll let you know when the Roots course is ready. All the best, Stephen.