This document outlines 5 times when not to ask for a raise. These include in your first year, if you want to leave, after a big win, when your boss is stressed, and if unprepared. The key points are that your boss will consider if a raise is justified based on how it saves or makes them money long term, not just a single win, and the worst times are those that don't show commitment or come across as opportunistic rather than earned.