Three most important skills?
1) The ability to troubleshoot effectively. This is the kind of thing you must learn through experience. The ability to troubleshoot is invaluable in ALL aspects of IT. This is how you fix problems you've never
seen before (which you will come across often).
2) People skills. If troubleshooting wasn't so important to the actual job, I would venture to say people skills is THE most important thing for a desktop tech to be good with. More often than not, as a desktop tech, you will be dealing with end users directly, and as many techs I've worked with will joke: the most difficult aspect of computer repair is the users. You need to know how to deal with all kinds of people, especially the ones who think their smarter than you.
3) Experience doing the work. This is sitting at home tinkering with your own system, building your own system, breaking your own system and fixing it. This is working on multiple different systems for friends and family. Being comfortable fixing problems. On the job experience is best obviously, but even with none of that - home user experience can also be valuable. Certs are great, and they may help you land that job, but experience will ALWAYS run circles around certification. I might substitute experience for passion, because passion for computers is what keeps the best IT techs up at night learning new tricks, learning new things in their trade, and expanding past the desktop technician position.
To me, these are the 3 most important traits, coming from a tech that has more experience than training.