How do you get your boyfriend to stop being mad at you?

I'm assuming you mean if your boyfriend is angry WITH you rather than taking his anger out caused by something else ON you.

As with any situation that could lead to an argument, don't contradict him. Make sure he knows you appreciate anything he says and have taken them into account, from there on just compromise with him until the solution suits you both. This way he should no longer be angry because the cause has been dealt with. If he is being unreasonably angry with you for no reason, consider whether you really want to spend the rest of your life with him and if not it is better to break up with him now really.