Hardmode changes the pace of progression. The best preparation is not trying to predict every future need; it is making your world easy to navigate, organize and recover in before the difficulty increases.
1. Clean up the base before the transition
Organize storage, group key crafting stations and make frequently used supplies easy to find. A clean base reduces confusion when new materials start arriving.
2. Improve travel routes
Connect important areas with safe and recognizable routes. Faster travel makes repeated material runs and recovery much less frustrating.
3. Stock practical recovery supplies
Keep food, healing, spare equipment and common building materials accessible. Do not spend all your time hoarding; focus on items that shorten recovery after mistakes.
4. Finish the tasks that simplify your world
Complete any obvious infrastructure or exploration tasks that you already know you will want later. Entering Hardmode with fewer unfinished chores gives you more room to focus on new progression.