In ArchiCAD 10, Graphisoft introduced Guidelines to help geometry construction.
The workflow was simple, and was very useful.

In ArchiCAD 15, the workflow changed somewhat, but (personally) wasn't taken as a huge step forward.
Recently, more keyboard-based workflows have crept into my Guideline workflows!!!

As well as our previous tip on Guidelines in ArchiCAD 15, another point that does help smooth Guideline creation is the option of 'Force Guide Line Display'
While working in ArchiCAD 16, and using the default Work Environment, this shortcut is assigned the keystroke Q (as opposed to the tilde ~ key previously)

Force Guide Line Display invokes a number of options depending on location of cursor.
While working in any command/tool:
• If the cursor is on an 'edge', press Q and a guideline is placed along that edge
• If the cursor is on a 'point' or 'node', press Q and the cursor switches to allow a guideline to be placed in any direction, and returns to the tool workflow post-placement.

Variations on this idea are the classic combinations(introduced many moons ago) :
• Alt+X and Alt+Y which lock the X and Y axes and place a guideline at the current cursor position in the chosen axis.
• Alt+D or Alt+R which locks the radius or distance value and places a guide circle at that radius or distance
• Alt+A which locks the current angle and places a guideline along that angle