Backup, Backup, Backup
Always, always, always back up your site files and database. Most web hosts provide some form of control panel that you can log into and perform common administration tasks such as submitting a full site backup, files and databases. It is always good practice to produce these back-ups so that you may quickly restore back to your previous condition in case you mess something up.
Another helpful tip that we learned rather quickly is to create a development/test environment right on your local PC/laptop to mirror that of your production site. There are entire WAMP/LAMP environments available today, such as XAMPP from Apache Friends, which make this incredibly easy. This type of set up gives you an opportunity to test all of your site updates off-line prior to going live. Call it a dry-run, trial-run, or just being smart, whatever you like.
We will eventually place the upgrade instructions here and remove from the distribution, but for now, read the README.txt file FIRST and then UPGRADES.txt.