The aim of root cause analysis is to identify the factor(s) that resulted in one ore more past events. Often the event is unwanted and by identifying the root cause it is possible to prevent the event from happening again. There are several tools that can be used for identifing root causes. You can start with Process Mapping (PM) in combination with preparing a Thought Map (TM) or A3 in order to structure the problem solving. Depending on the problem I use various tools like Fishbone diagram / Cause and effect diagrams, Factor analysis and Pareto analysis.
Please note that root cause analysis is only relevant when the unwanted event is due to special variation. If the normal variation is causing unwanted result(s), you cannot look for a root cause. Overreacting to normal variation by adjusting, will likely worsen the situation. Statistical process control (SPC) is used to distinguish between normal and special variations to respond correctly to measurement results.