To perform a clean install of Lion, you must have a disk or partition available that uses the GUID Partition Table and is formatted with the Mac OS X Extended (Journaled) file system. The target volume should be erased at best; at a minimum, it should not contain any OS X system.
With previous versions of OS X installers, you could erase the target drive as part of the installation process. With the Lion installer, there are two methods of performing a clean install. One method requires you to create a bootable Lion install DVD; the second lets you perform a clean install using the Lion installer you downloaded from the Mac App Store.
The difference between the two methods is that in order to use the Lion installer directly, you must have a drive or partition that you can erase prior to running the installer. Using a bootable Lion install DVD allows you to erase a drive or partition as part of the installation process.
If you wish to use your current startup drive as the target for a clean install, you'll need to the use the bootable Lion install DVD method we outline in the following article:
If you're going to perform a clean install of Lion on a drive other than your current startup drive, then you're ready to proceed.
Perform a Backup
Before you begin the Lion installation process, it's a good idea to back up your existing OS X system and user data. Performing a clean install on a separate drive or partition shouldn't cause any type of data loss with your current system, but stranger things have happened, and I'm a firm believer in being prepared.
At a minimum, make sure you have a current backup. For a bit more protection, make a bootable clone of your current startup drive. You can find the method I use in the following article:
Format the Destination Drive
You must erase the target drive before you can start the Lion installation process. Remember that to use the Lion installer as downloaded from the Mac App Store, you must have a working copy of OS X to start the installer from. This means you may need to create a new partition to install to, or resize existing partitions to create the necessary space.
If you need instructions for adding, formatting, or resizing a drive's partitions, you can find them here:
Once you complete the preparation on the target volume, you're ready to begin the Lion installation.