PAT is so intimidating and tough at the beginning, and the only thing that will make it better is practice, BUT IT WILL GET BETTER! Also for cube counting specifically, the tally method never really worked for me, I think it was just too much to think about after finally deciding how many sides were painted per each cube. What I found works amazing is just kind of "mapping" out the cubes on your paper; I just start at one end of the structure and count how many faces per cube and I just start writing down the numbers on my paper without actually ever looking down at the paper. For example let's say you just had a column of 5 cubes stacked on top of each other, I would just start at the top of my page and write "5", then move down the column on my paper with "4 4 4 4". This also makes it easier to go back and see if you made mistakes because you can actually see which number corresponds to which exact cube, instead of just having a list of tallies to look at. Hope this helps
