Always focus on high-frequency words. Never waste time on other words or terms. One can obtain a list of high-frequency words for various fields, just be searching the internet. Also, one can use linguistics software to examine a book, and then create a frequency table of most-often occurring vocabulary, using a spreadsheet, and least-common occurring vocabulary. This, as you have stated, is a very efficient approach. Also, I should know about the most efficient strategies for L2 and L3 learning because...after all... I am a genius, as I have mentioned previously, a few times.