It is not that I'm an expert and maybe those tips are obvious for you but still:
- when working with model switch off all the layers you don't need to see at the moment like moldings, furnitures, decoration etc.
- like above but when working on plan (all fotos, backgrounds, pics, 2D drawings should have seperate layer)
- for the moldings - I found that nothing slows down calculation more than objects from outer modelers (I'm using ArchiForma), just look at weight of the objects you have created - everything bigger than 250kb is bad. Make sure you are using those only if there is no way to model something with ArchiCAD native tools.
- for the material library - DO NOT load all the materials, only those you're using in the project. I found myself having over 300 mat. in the library and using only 10-12 same time. I made a separate, simple test scene where I play with materials and when I'm satisfy with the results I simply add it to my 'custom materials library' with the '!' in front of name. This way you have them always on top of the list and can easly distinguish them from the others.
- if you're not planing to render baners, app. 1200x800 texture maps is more than you need (just my experience)
Hope this helps.
Cheers