Well, in my desire to get more serious about learning my openings I have started to make opening flash cards. Not really flash cards in the traditional sense of the word, but index cards with lines and variations.
i.e. I just made a set on the Ruy Lopez Closed Worrall and the format is like this...
On the front of the 3"x5" card at the top is Ruy Lopez Closed Worrall (...9. Bg4 & 10...Bh5). Then, below that are the initial moves of the variation: 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. Qe2 b5 6. Bb3 Be7 7. 0-0 0-0 8. c3 d5 9. Rd1. Then below that in bigger print is 9...Bg4
On the back is the rest of the line: 10. h3 Bh5, etc.
The next card is the Ruy Lopez Closed Worrall (9...Bg4 & 10...Bxf3) with the same moves on the front, and then on the back 10. h3 Bxf3, etc.
Why do I do things this way? Because for me it's easier to prep openings by glancing at the cards and playing through the moves rather than playing through your typical tree of variations opening books which has all the extra sub-sub sidelines, etc. between the main stuff that you need.
I can play through the dozen or two lines that I feel I might need to brush up on for a particular opening in just a handful of minutes rather than spending an hour working through a book that has a lot of "clutter" in it.
I know that these days a lot of people just use Chess Openings Wizard or similar technology to help opening prep. I'm all for that and will probably eventually begin using that but for now this works just fine.
I'm interested in hearing how others prep their openings.