Don't Install macOS Mojave if You Only Have One Mac
Don't install the macOS Mojave beta on your Mac if you only have one device. This is a beta that will have problems. There is a good chance that something you do every day will not work as good as on macOS High Sierra, and that there will be battery life problems during the early beta.
This could prevent you from getting work done or even using your computer. Specifically you should not use this on production hardware at work or at home.
The best thing you can do is install the macOS Mojave beta on a spare Mac, even if it is an older model that you don't use every day. This allows you to test the new features and test Mojave without worrying about your data and computer.
Another option is to make a second partition and install the macOS Mojave beta so that you can dual boot between macOS High Sierra and macOS Mojave. You need to have enough space on your drive to do this.