Prepare for an opponent by narrowing uncertainty within a repertoire you already understand. Review a small set of their available recent games, paying attention to colour and time control. Identify repeated opening choices, but treat the sample as evidence rather than a guarantee. Your opponent may change lines, have unpublished games, or prepare specifically for you.
Choose one likely branch and one fallback. If you play the Ruy Lopez and the opponent often chooses the Berlin, review the resulting positions and your intended response. Decide whether you want the main endgame or a quieter d3 system. The choice should reflect your preparation and comfort with the position, not just a database percentage from a small sample.
Study the first decision where your preparation differs from your normal routine. Check forcing replies, typical exchanges and the plan after the opening ends. Avoid spending the whole session on a trap that works only if the opponent makes an unlikely mistake. You need a playable position when they respond well, and a plan when they choose a different opening entirely.
Before the game, reduce your notes to a few key reminders and test them from the board. Respect event rules about outside assistance: preparation belongs before play, not during an unauthorised live game. After the game, compare what you expected with what happened. Keep the useful structural knowledge even when the predicted variation never appeared; it can strengthen your repertoire for future opponents.
Try this at the board
Pick a likely opponent reply, select your planned variation, and name a sensible fallback if the prediction is wrong.