How I finally stopped mixing up 大切・大事・重要

These three all mean "important" and I used to just pick one at random. What helped me was sorting them by "warmth": 大切 = precious, something you cherish emotionally (家族は大切です — family is precious to me). 大事 = important, often with a "take care of it / handle carefully" feel, and it's the one used in the set phrase お大事に (take care, said when someone's sick). 重要 = important in a formal, objective, businesslike sense — the one you'd see in a news report or a work memo (重要な会議, 重要な情報). So: 大切 = heart, 大事 = care, 重要 = report. Doesn't cover every edge case but got me through 90% of usage.