Find the cause of the column does not exist error from the five usual ones: a typo, double quotes, an alias in WHERE, a quoted name and a missing table. After this, you can fix it in a minute instead of changing the table.
Read the error, then fix it the right way: group by the column, aggregate it or move the aggregate into a subquery. After this, you know which fix keeps your numbers correct.
Run one slow query with EXPLAIN ANALYZE and read it with a five-question checklist: rows touched, filtered rows, estimates, loops and sort spills. After this, you can find the slow node of a plan and check your fix.
Turn on pg_stat_statements in a Docker container and list the statements that cost the most in total. After this, you know which query to tune first, and you do not have to guess.
Reproduce a deadlock between two money transfers, read the message, and fix it by locking rows in the same order. After this, you can turn a deadlock detected error into a plain wait.