Speaking is the most important skill and actually the only skill that is necessary.
You don't need working speed at all because when you can't take anymore work, you can simply change the language, and then all task requests from your boss will be all gone.
You don't need health at all because when you do any thing that cost your health, as long as your health is more than 0, you will be safe, so you just need to watch your health and do things once you have at least 1 life, you will always be safe.
You don't need challenge until you become a president of a company because challenge only provide you some quick money and higher promotion chance when you collect all ways to be fired. The quick money can be obtained by changing your system time and do part-time jobs repeatedly. The collection bonus will be not useful until you become a president anyway since one of the "fired collections" requires becoming a president.
Comment found on Don't get fired!: what to upgrde first
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.
Comment found on Don't get fired!