My First question comes from - SilverShadow of the Pagan Rapport (@CriticalFault)
Like many things with workings I believe that this is a matter of personal preference and based on your own accepted symbolism. I personally tend to use equal arm crosses or "crossroads" quite often, and triangles both in candle configurations, and when laying out certain materials. I use the cross because it symbolizes a metaphysical space and point where all possibilities can be achieved. I use he triangle as a space where spirit can manifest. So my two main go to configurations are a mix of hoodoo lore, and ceremonial magic thought. Occasionally I will use circles of candles to represent protection as well. If you have a fondness for ceremonial magic or Kabbalistic thought, that can certainly be incorporated into candle workings especially if you are utilizing planetary energies. I would recommend the "Golden Dawn Lecture on Polygrams and Polygons" for reference. In regards to Hoodoo a lot of the candle configurations that you will see are influenced by or come directly from books such as the "Master Book of Candle Burning" by Henry Gamache. In my opinion there are no set rules on this. If it feels right, then do it. If it gets results, do it again. If not, then back to the drawing board.
"I wondered about geometric placements of candles, incenses, etc. Often you
see people post images of their ritual workings and their materials are
setup in circles, triangles, squares etc. I wondered if you had some insight
on how to use these shapes within a ritual context and what those shapes
meant when they are applied!"