My recommendation has always been:
1) Work through the Archicad Learning Guide from ArchVista to get a general idea (total time: 8 to 12 hours if you are in a hurry, 16 to 20 if you move more normally)
2) Take a classroom training (total time: 2 to 3 days)
3) Read this forum. You will find a huge back log of information. If you have specific questions, you can usually get answers. General ones like "How do I use Archicad?" may not get much, nor will ones that are covered in the basic tutorial ("Where do i set the wall height?").
4) Build a relationship with a reseller or consultant you like. How much should you like them? I hear Link has a fan club....
The first two should get you up and running and be mostly self-sufficient. Number 3 is a nice free fallback.
Beyond that, you will run into brick walls and impasses and it helps to have someone that you know can bail you out quickly if you need something fast or if you are really in a bind. It's nice to know you have the safety net.
There will also be times where you wrap up a project and want to know how you could do the next one more efficiently and you know there's a way, but you need a little guidance.
Good luck, and welcome to the community!
Tom Waltz
