Pick a drive, that has a fast connection - USB3 or Thunderbolt, if your mac does support it. Use a locally connected drive, not a NAS: Use locally mounted Mac OS X Extended volumes for your Aperture library
Make sure, your drive is formatted MacOS X Extended (Journaled).
To move the library to a different drive, repair it, before you copy it. (Repairing and Rebuilding Your Aperture Library). Update your backup, before you proceed.
To change the location of the library, you move the library file to a new location (drag it in the Finder) and then double-click it to open it in Aperture. Test it thoroughly, before you delete the old library from your system drive.