Reproduce the defect
Before you can fix a defect you have to be able to reproduce it. It is very rare for a defect report to be good quality, so once you have found a way to reliably reproduce the defect modify the ticket that raised the defect with details of how to do this
Work out what is causing the defect
Often this will be obvious, and just as obvious this won’t. If it is difficult to recreate, consider making an acceptance test for the defect. This will be deleted later but may help during the early stages.
Make one or more unit tests that capture the defect
Acceptance tests are not valuable to us: we want unit tests. Once you have a failing unit test you can follow the advice in done it a lot before