As others have posted(myself included), things you should try BEFORE you try doing the update:
1) Uninstall antivirus on your phone since this can cause problems with the update
2) Turn off any firewall software on your computer
3) Enable USB Debugging on your phone(under settings -> Developer options)

I also suggest uninstalling any launchers, such as nova launcher, and any keyboards you may have installed on your phone. You can install them after the update, but it is POSSIBLE that these could cause some issues.

Since there are so many apps out there, it may be necessary to do a factory restore AFTER the update if you find things are acting strange. Since so many apps set themselves up to run in the background continually, you may not even realize they are there and causing problems, so that is why the factory reset will fix problems in some cases.