Step 1: Make sure your Mac is up to snuff

Unfortunately, Leopard is going to have some serious hardware requirements. From Apple's site:

• Mac computer with an Intel, PowerPC G5, or PowerPC G4 (867MHz or faster) processor
• 512MB of memory
• DVD drive for installation
• 9GB of available disk space

Step 2: Back up, back up, back up!

Okay -- you should already be backing up on a regular basis, but if you haven't been, now is absolutely the time to start. My preferred backup regimen is to make a complete bootable clone of my main hard drive, which is updated automatically each night (a "differential" backup). The advantage of this is that you can immediately recover from a hard drive failure by booting your Mac from the external disc by holding down the option key at startup.

I swear by the excellent SuperDuper! ($27.95) for my backups, but the same can be accomplished with the donationware Carbon Copy Cloner as well. You'll just need to get an external hard drive (I recommend FireWire, but USB will work), and set the application to run each day in the middle of the night or whenever else you're not using your Mac.

Folks have many different opinions on which drive to get. Apple, for instance, seems to be showcasing the nice, but slightly more expensive G-Drive from G-Technology. Nonetheless, just about any decent external FireWire drive should work well.

But, you say, Leopard will have Time Machine for backups! Indeed it will, and one of the requirements of Time Machine is an external hard drive. So you'll be in good shape if you go get an external drive now and make the bootable clone. This clone can also serve as the source of your user data for reimportation via the Migration Assistant after you install Leopard.

It's not entirely clear yet how Time Machine works, but it appears that it will take advantage of whatever hard drive space you have to make its incremental backups. Therefore, you should get an external drive at least as big as your internal drive and probably as large you can comfortably afford. See our recent Leopard Spotlight for more information on Time Machine.

Personally, being a bit paranoid about my data, I make two full bootable backups, but that's probably overkill. External drives are cheap and my data is very important to me, so it's worth it to me. Once I get Leopard installed I'll likely keep two external backup drives connected to my Mac: one to use with Time Machine and a second to use with SuperDuper for a full differential backup each night. Even with Time Machine installed, having the second cloned drive can still be very handy because it minimizes downtime should your internal drive fail; you need only to reboot the machine with the option key held down to get going again. You can then replace your internal drive as soon as is convenient.

Step 3: Maintenance

Optional. Okay there are a variety of schools of thought on maintenance and I don't want to get into any fights (see for instance this post from a while back). Nonetheless, I would suggest having a look at the free applications MainMenu and/or Onyx.

Step 4: Consolidate and clean up

Now that you've got your full backup, it's probably a good time to do some Spring (or Fall) cleaning. You might start with this nice little application WhatSize, which will help you find all largish files you might have forgotten about and no longer need. Just go through your drive and pare down whatever you don't need.

Step 4.5: Optional, eliminate unneeded applications.

Once you've cleared away old files you may also want to delete any old applications you no longer use. However, it's best not to just drag them to the trash as that will tend to leave preference and setting files. I delete applications with AppZapper ($12.95). AppTrap is a similar donationware alternative.

Step 5: Update your applications with AppFresh

Now that you've cleaned out the dead wood it's time to make sure all your applications are up to date. Many developers have been pushing out updates to make their applications Leopard-ready. Keep in mind, however, that Leopard many very well break some applications (e.g. there's been talk about Adobe CS3 incompatibility). If there are any absolutely mission critical applications you need, you may actually want to hold off upgrading to Leopard until you're sure that they are compatible (check with the vendor).

The easiest way to make sure your applications are up to date is to use the clever AppFresh from metaquark. This application is still in beta, but it already works quite well. It will scan your machine for all the installed applications (including Preference Pane apps) and compare the version numbers to those listed on iusethis.com. It will then allow you to download and install any available updates.

Step 6: Back up again!

Now that your Mac is up to date and in good shape, it's time to back up again. You should be able to just do a differential backup - "Smart Update" in SuperDuper.

Step 7: Wait impatiently for Leopard

That's it, you should now be ready for Oct 26th. Keep in mind my proviso above about making sure your mission critical applications are compatible before upgrading. If you're sure your backup(s) are good - boot off of them just to make sure - I'd go ahead and do a clean installation of Leopard then re-import user data with the Migration Assistant (from your external hard drive). If you've got the space you may choose to Archive and Install instead. I know some folks choose Upgrade, but I personally prefer to start fresh because I install and delete a lot of software as part of my work here on TUAW (as you might imagine). Nonetheless, if you're less concerned about cruft than I am, the Upgrade option may work out fine for you.

Step 8: Start wondering when OS X 10.6 is coming out