Starting Thursday, Apple will be sending out invitations for the OS X Yosemite public beta. If you're hoping to be one of the folks who gets it, this is a good time to make sure that your Mac is ready for the big event.
First of all, bear in mind that OS X Yosemite is already on its fourth developer preview release. They've been coming out every few weeks since WWDC in early June, and they've been getting progressively better. But OS X Yosemite is still very much a beta.
Because it's still in development and because it's the bedrock operating system of your Mac, you shouldn't install it as your primary operating system. If you have a spare or secondary Mac you can use instead of your primary one, that's a much better idea.
Before you do anything, you absolutely must back up your Mac. Whether you use Time Machine, a disk cloning tool or a remote backup service doesn't matter — just make sure all your critical files are safely backed up before you make any major changes to your operating system.
- How to easily back up and restore your Mac with Time Machine on OS X Mavericks
- How to easily clone your Mac using SuperDuper! or Carbon Copy Cloner
- How to easily backup (and restore) using BackBlaze or CrashPlan
Where to put Yosemite
If you do not have a secondary Mac to use, the best idea is to install Yosemite on a separate hard disk drive connected to your Mac. After you download the installer, simply tell it to use the external drive as the installation target, then let it rip. Afterwards, you'll be able to reboot from your Mavericks drive by holding down the Option key on your keyboard on boot.
If you can't afford or don't have access to an external hard drive, you can install Yosemite on your internal hard drive, but again, don't make it your primary operating system. This is cutting a bit close to the bone, but the safest thing to do is to set up your drive with multiple partitions - one to run Mavericks, and another to run Yosemite.
One last tip: If you can avoid it, I'd recommend not to copy over settings or files from your existing partition. This is called doing a "clean install" of Yosemite. Once Yosemite's ready for prime time, it'll probably be safe to do a data and settings migration from your existing Mavericks installation. But for now, it's good to rule out any old baggage as the source of potential problems while you're testing software, so make sure to leave that stuff out if you can.
The Bottom Line
Between backing up, using an external drive or, if necessary, partitioning your Mac with a separate Yosemite partition, and doing a clean install, you can safely test the Yosemite public beta without a huge amount of risk to your Mac in the process.
By all means, have fun with the public beta, put it through its paces and get to know this new software — Apple's promising some great things with Yosemite and iOS 8 together once they're out in the world, and it's great to be giving a chance to put Yosemite through its paces early.