I thought of a way to make money without working so much (thus downing your chances of getting fired for something): when you are in one of the menus - say looking at your promotion chances or skill set - your in-game timer stops (so if you have work waiting, you won't get in trouble for not answering), but crucially, the part time job counter continues (which it doesn't if you lock the screen or press out of the game). So you can actually spend all the waiting time in the menus and go straight from part time job to part time job to build up that money and buy experience and skills!
It's kind of slow, but you make money faster when your bosses aren't constantly approaching you to buy them wedding gifts or presents for their brat kids. Your mum also can't bug you for a $10000 purse. Selfish betch.