Follow your Irits.
Sometimes the I should help people stop fighting, and sometimes the I should step back. In addition to your Irits, also consider the situation, especially if the I is talking about a physical fight. The I might get hurt badly by getting into the middle of people fighting. And it doesn't make sense to get yourself hurt over somebody else's wickedness.
In regards to people doing something wrong. Again, the I should firstly follow your Irits. If the I tells people too many times that they are doing wrong, then they will eventually stop listening at all, or might fight against the I. Some people don't want it to be revealed to their own mind that they are doing wrong, and will try to stop those that reveal it.
It is also good to not tell a person that they are doing wrong in public, or they will likely not listen because of their embarrassment, and will listen even less in the future because of the resentment they will have because the I embarrassed them.
Here is a reasoning that shows the scripture that speaks about the duty of the WatchMan and WatchWoman.
Also, look at this topic I just posted, it is from a reasoning I made a long time ago.
Know When to Speak