Potions are one of Terraria's most practical preparation systems because they can improve survivability, damage, mobility, mining and exploration without permanently changing the build.
Boss preparation
For difficult bosses, focus first on buffs that improve the weakness actually ending your attempts: survivability, movement, damage uptime or resource management.
Exploration potions
Some potions are more valuable outside boss fights because they reveal resources, improve movement or make dangerous environments easier to navigate.
Mining and resource runs
Mining-focused buffs can make a short targeted run more productive. Combine them with a clear material goal instead of using valuable consumables during unfocused exploration.
Do not overprepare
If a boss is already manageable, adding ten more buffs may create more farming work than value. Start with the few effects that matter most and expand only if the fight still exposes a weakness.
Keep a repeatable supply
A good potion plan is sustainable. Store commonly used ingredients, grow what can be farmed and keep a small reserve for bosses instead of crafting from zero before every attempt.
Source: Official Terraria Wiki — Potions.