I've been making opening preparation software for 35 years and I finally got bold enough theorize what is behind success in preparing openings.

So I made a video. A long one.

Full disclosure: the video ends in a commercial for my software (Chess Openings Wizard) but the two habits that I've found are essential can be done on paper as I point out in the video.

http://www.bookup.com/ChessOpeningsWizardProVideo.html