1) Look at New Features
CircleCI releases features at a fast pace and there may be something new that can help your project. Check the changelog for new features and see if any can help with your use case.
2) Check the Configuration Reference
The configuration reference is a list of all configuration keys available in a CircleCI config file. It can be useful to read through the right sidebar and see if any keys are of interest.
3) Record Features of Interest
Record any features of interest for reference throughout the config review. If any recorded features are found not to be helpful, note why for future reference.