Quick guide / tips (going through attribute manager):
for layers try to stick to your national standard (assuming it exists) and add layers for annotation at different scales, layers for sections markers, elevation markers etc and layers for different type of zones
you want layer combination for plans, sections, elevations, details etc, most likely at 2 or 3 different levels of development stage
I would stick with the pen set your version of Archicad ships with. Reason being: if you load your library all the parts will assume certain pens are being used in a certain colour and pen thickness
Also stick with the default line types. I can't say I've ever added anything custom here.
For fills, also start with the default fills and add what you are missing. Do not change the default ones, because again: library parts will assume certain fills look a certain way
Start with the default surfaces and add what you are missing. There are more surfaces that you can add from the library.
Building materials: again start with the default and expand. I typically have 2 or 3 levels of priority 'strength' per type. For example concrete in a 500 range and in 900 range. You will find that you will need this to solve most common connections.
Populate composite and complex profiles only with the ones you will use a lot, or the list will become too large to manage. You will always add project specific composite / complex profiles, these should not all be in the template, in my opinion.
You will probably want zones for building type (residential, industrial etc), fire rated zones and room function (living space, corridor, etc)
The last attributes can just stay default (markup, cities etc)
After this we have setup a typical floorplan with gridlines and dimension and a few stories for the model.
Then we have viewsets predefined for the sections, elevations and floorplans. We have all the different design stages pre-defined here.
Finally, we have master layouts for different page sizes and pre-linked layouts for the design stages.
This is a very quick write up and rough guide. You will most likely find a lot of the same principles in Shoegnome's template, however his template would assume that you are using the US library and my guess would be that you have the international version and there might be differences.