What can I do to avoid problems when installing SP1 for Vista?

Prepare your system software.

Be sure that no other applications are running, especially security apps like anti-virus, anti-spyware or firewall softwares. Disable these for now, and re-enable them after completing the SP1 update.

If your motherboard uses an NVIDIA-based chipset or an Intel network adapter, you may consider downloading the latest versions of these to reinstall after installing SP1.

Next, prepare your system hardware.

Disconnect any external hardware devices you may have added, like printer, storage, mp3 player, or bluetooth devices.

Again, if your motherboard uses an NVIDIA chipset or an Intel network adapter, you may consider first uninstalling these prior to installing SP1. Reboot.

Then, install SP1

The service pack installation will after a while require a restart, after which the update will resume, and then be followed by another restart. Once the update is complete, reinstall from your downloads any drivers you may have uninstalled. Re-enable your security software. Check Windows Update for any further updates.

Note that if you do encounter a problem, free support from Microsoft is available:

Unlimited installation and compatibility support is available for Vista SP1 at no charge until March 18, 2009.