I've worked in many different environments (sales, finance, banking, training). I have also been fired from a job before (not immediately, but after several warnings) for tardiness. I would say a good golden rule to live by is "always be honest". Integrity will always guide you in the right direction- to do the right thing. Different companies may fire for different reasons, it all depends on their policies. As stated in other answers you got on your question generally actions of dishonesty (stealing, using company resources wrongfully, lying to customers, abusing power, etc) can cause someone to get into deep trouble fast. No matter where you work a great way to stay out of trouble is to stay informed and updates, and ask questions. If you don't know whether something could get you in trouble, ask someone before doing it (manager, peers) or read up on their policies.