One way is to write them down. Just take a notebook and start jotting down the stories that your grandparents or older relatives tell. This way, they can be passed on to future generations.
Another important aspect is to incorporate these stories into family traditions. For example, during family reunions, ask an older family member to share a 'good old days story'. This not only preserves the story but also makes it a part of the family's cultural heritage. Additionally, local historical societies can play a role by collecting and exhibiting these stories in the form of written accounts, audio - visual displays, etc. This helps in spreading awareness about the significance of these 'good old days stories' in the community as a whole.
Recording oral histories is also a great method. Use a voice recorder or your phone to record the 'good old days stories' as they are being told. You can then create a digital archive of these stories. And also, encourage schools and local libraries to be involved in collecting and preserving these stories so that more people can access them.