Don’t Install if You Aren’t Prepared
Are you ready to install macOS High Sierra on your Mac? If you had to think about that, you probably aren't.
At the minimum you need to have a good backup for your Mac. You won't likely need it, but in case something goes wrong, you will want to have your Mac backed up so you can restore. This may be Time Machine, or another service. Whatever it is, make sure you have a backup.
We also have a full list of things you need to do to get prepared for installing macOS High Sierra on your Mac. This includes checking what apps work with it and if there are any compatibility issues with your favorite accessories and macOS High Sierra.
With new features and a new file system this is important to check before you upgrade. Be prepared so you can upgrade smoothly instead of scrambling later.