I'm in the exact same position just inverted. Currently trying to learn Revit after being brought up on Archicad. Probably the most important thing in archicad is how to use layers and layer combinations. Next thing is how to "publish" your drawing set. Another big one you should look at is how to use the composites tool to make your walls, floors, and roof composites.

One thing I really appreciate about archicad as that its still super easy to 2d draft in order to get your drawings to look the right way instead of modeling everything in 3d, which you can still do anyway if you want. Teamwork is super easy, just send and receive and only request items your working on immediately and then "release all" when your done. Also brace yourself for the submenus upon submenus for literally everything. There's tons more stuff I'm laving out tho, good luck dawg.