I have had a lot of sims get promotions by asking. None of them had the Brave or Ambitious traits. As far as I can tell, the secret is their performance meter needs to be almost at the top and, of course, a good relationship with the boss. Invite the boss over, talk about work, and pretty soon they will get the options to Ask for Promotion and Ask for Raise. If you get a promotion early in the day before going to work (like the cooks, who work evenings), then they don't have to go to work that day. I was very surprised the first time this happened - I kept trying to get my sim to go to work and wondering where the carpool was. I finally looked at the Career tab and found out she didn't have to go to work until the next day.