Hello Mike,
Some references state that there are about 500,000 words mounting to 1 million including scientific words. However an average educated person knows about 20,000 words.
You can check this table for further references in detail:
http://hypertextbook.com/facts/2001/JohnnyLing.shtml
Some methods to increase your vocabulary and memorize them effectively:
- Read texts and books at your level of comprehension and look up new words .List those words in
categories such as office vocabulary , animal life vocabulary , emotions etc.
- Listen to a lot of English through different medias: song lyrics , watch subtitled movies , online
audio material etc.
- Converse with native speakers ,don't hesitate to ask for new words you don't know before.
- Read loud ,record your voice , listen to it and keep repeating the process using each time more
intricate texts with more difficult vocabulary.
- Do any activities that involve using the English language , such as games, quizzes .
- Switch all your operating systems on devices and gadgets to English, so you would be always
reading your instructions in English.
- Make a trip to an English speaking country , visit their museums ,mingle with their people.
Immersing yourself in the culture will be a good motive for you to learn more later.
Good luck:)