Most of the "best practices" floating around right now are already outdated. Opus 5.5 changed enough that your old prompts are quietly costing you more than they should. Here are the shifts worth knowing: On effort levels ➤Start at medium, not high. It's now the sweet spot between speed and quality for most tasks. ➤Don't guess, test. Run the same task at low, medium, and high once and see what your workflow actually needs. ➤You can now switch effort mid-conversation without the model re-reading the whole chat from scratch. That used to be expensive, now it's just a setting change. On instructions and memory ➤Claude Code now reads a single agents.md file. No more juggling between claude.md and agents.md to keep in sync ➤In long chats, tell the model to treat earlier answers as settled. Otherwise it keeps re-checking old decisions instead of moving forward. ➤Have it keep a running checklist for multi-step tasks. Example: think of it like a to-do list taped to the model's desk, it stops it from marking a task "done" when it's actually 80% done. On pacing and cost ➤Give it a time budget. Saying "finish this in 3 minutes" actually changes how it paces the work. ➤No specific budget in mind? Just add "time matters." It speeds things up on its own. ➤Check your settings for free usage resets that came with the 5.5 launch, easy to forget, easy money left on the table. On design and images ➤Give it an actual design system or brand guideline. Without one, it defaults to generic, forgettable output. ➤For image-heavy tasks, let it crop and zoom using tools like PIL or OpenCV instead of processing the whole image. Smaller, sharper crops mean fewer tokens burned. ➤One more thing to know: asking it to "show its reasoning" may get flagged or refused more often now, so build that into how you test outputs. Which one of these are you not doing yet, the checklist, the time budget, or the effort testing?