Then perhaps using something like A3, which provides guidance on the steps for defining the problem, finding out why it occurred, developing and implementing countermeasures, and seeing how well they worked.
8D is then a more comprehensive model, but I wouldn't recommend it for beginners. It was designed for more complex situations.
My 10-step model parallels both A3 and 8D, but is stronger, more detailed in the steps for finding causes.
ASQ has some good info on RCA on their website, including webinars, examples, etc.
Also, financial auditors to RCA as part of their audits when they find a nonconformity. Seeing how they do this can also provide ideas that can be translated into quality process applications.