These books on the subject of term sheets are solid

https://www.amazon.com/Term-Sheets-Valuations-Intricacies-Bi...

https://www.amazon.com/Venture-Deals-Smarter-Lawyer-Capitali...

http://web.mit.edu/tytso/www/OPTIONS-HOWTO/OPTIONS-HOWTO.htm...

https://news.ycombinator.com/item?id=2623777

https://gist.github.com/jdmaturen/5830b83c1425c4767f7e1bd4c9...

https://github.com/jlevy/og-equity-compensation