This is a short tutorial on how to update your Mac OS X system software. If you follow these steps, you should have a successful updating experience.
(1) Download the combined updater from Apple's website. Many people who have had difficulties with updates have either updated with Software Update or used the single update file, so, to be safe, use the combined update.
(2) Remove any plug-ins you might have added to system software applications such as Safari or Mail.
(3) Launch Disk Utility and repair permissions on your boot drive.
(4) Run a maintenance program to clean caches and run the Mac OS X daily, weekly and monthly maintenance routines. My favorite program is Onyx.
(5) If you own a backup hard drive, clone your main drive to the backup drive and test the backup drive.
(6) Turn off all your computer equipment and disconnect third-party peripherals (hard drives, CD/DVD drives, etc.).
(7) Turn on your computer and install the Mac OS X update from the standalone combined updater.
(8) Restart your computer. Be patient while the computer restarts - this might take a few minutes and your computer might do a double restart. Don't panic, this has been the normal procedure with the last few Mac OS X updates.
(9) Run DiskUtility and repair permissions one final time.
(10) Reconnect your peripherals and enjoy the update improvements.
Remember, with any new system update, it's always a good idea to wait a few days after the update is released and read the Apple discussion boards before installing the update.