I always answer this when I'm asking myself ''do I have to stop?''
Universality test :
Find the agent's maxim (i.e., an action paired with its motivation). Take for example the declaration "I will lie for personal benefit". Lying is the action; the motivation is to fulfill some sort of desire. Paired together, they form the maxim.
Imagine a possible world in which everyone in a similar position to the real-world agent followed that maxim. With no exception of one's self. This is in order for you to hold people to the same principle required of yourself.
Decide whether any contradictions or irrationalities arise in the possible world as a result of following the maxim.
If a contradiction or irrationality arises, acting on that maxim is not allowed in the real world.
If there is no contradiction, then acting on that maxim is permissible, and is sometimes required.