Matt, there are guidelines for what and where. The unknowns are how many and how much (thickness/frequency coverage etc.)
It really depends on the room material/furnishings (sabin/absorbtion calc.) and dimensions (volume) and intended use. These determine the rooms target RT60. In practice I have found the biggest initial payoff was treating front corners with bass traps and treating first reflection points with broadband absorbtion. BUT all of these guidelines you will find online only apply to a normal rectangular room. Any absortion you put anywhere is supposed to lower the RT60, so the initial treatments have a double payoff.
RT60 used to be the only characteristic in planning/evaluating a rooms acoustic performance. Since then relections and our spatial/timing perception have become a focus in planning a space.
Both our rooms are constructed on resilient channel, and I have an optimistic outlook about bass response. Our walls should already be hugely useful in taming bass reverb. They should absorb and re-emit bass at a shifted frequency, hopefully helping with modal issues as well. Dunno yet.
One a side note, I found a recipe for building polys that many seem to have built and are happy with. I should mention the polys I'm building are for between the 1st and 2nd absorbtion points and were chosen because of their look more than their diffusion properties. They will appear as colums in the finished room.
https://www.gearslutz.com/board/attachme...poly-panels.pdf
