My six favorites:
The person who reads one great book twice is better off than the person who reads ten average books.
Teaching others is a powerful way to embed information in your mind. Upon completing a book, grab the nearest (willing) person and tell them about what you have learned.
If we read but don’t reflect, we only have the illusion of knowledge. Making the knowledge our own means digesting, synthesizing, and organizing the information.
The work of reading: Read a book while highlighting heavily. Distill highlights into core insights, written in your own words. Put it into a searchable format. Review regularly.
If you want new ideas, read old books.
Writing about what you read is the key to turning the experience of reading into knowledge you can use. Writing is reflection.