In step 1 we discussed gathering information. Without getting good information you are shooting in the dark. Make sure you take the time to know the system well enough to make educated guesses about what to try. That's our next step - trying stuff. I started out making a priority list... as in first try A, then B, but it soon became obvious that it wouldn't do to dictate the order in which you would attempt any of these changes.
In fact, some of these changes fall more under the auspices of "best practice" for configuration and you should probably do them regardless of whether they fix your problem or not. Still, if you are tracking a particular issue then you might need to try something, test, and wait for a result. So here are my “things to try” in no particular order. Your experience will have to help you figure out where to go first.