I'd recommend getting good training for about a week, regardless of any software background, if you are new to ArchiCAD.
We've had that for new colleagues and interns alike and they are so much more productive after a week training than having a look at some online videos or having someone else teaching along their work.
Professional training saves time and money in the long run.
Get a good template too, or use the one it shipped with and adjust it as needed.
On a side-note: we have a yearly upgrade training with our local reseller as part of our subscription and sometimes I meet people there who are trying to do 2D CAD in ArchiCAD and I just don't understand why you would throw away all the benefits of having a 3D model in favour of sticking what you are comfortable with.
Erwin Edel, Project Lead, Leloup Architecten
www.leloup.nlArchiCAD 9-26NED FULL
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