Have a backup and possibly two (Time Machine / Carbon Copy). It's going to work most of the time but just reading the forum here you can see for whatever reasons, it can mess up.
Yes backup of content on the Mac, and I suppose I should do this also ? In case something went wrong during installation ? Sorry, I've not done this before 🙂
Just run the installer.
Your only concern is whether all your apps will be completely compatible. Most modern apps should be, but some might need updating to versions (which may not quite be released yet).
If you prefer to sync your contacts locally and not use iCloud syncing don't upgrade. Apple now forces you to sync contacts through iCloud in Mavericks.
Have a backup and possibly two (Time Machine / Carbon Copy). It's going to work most of the time but just reading the forum here you can see for whatever reasons, it can mess up.
Also when it says less then a minute remaining and the bar is solid blue and completely filled in it is lying to you. I upgraded 2 mac's (an air and mini) where it was only a couple of minutes, but when I did my MBPr it stayed this way for over 15 minutes, so I forced a reboot, hence the need for the backup, MBPr booted up into recovery mode. Reading other posts (afterwards) it can take quite a while for it to actually finish.