For the last 20 years or so, I've been working on the "sew/cut large and trim down" theory. I find I get more accurate results and that it is easier and faster and ultimately more enjoyable for me to sew with less stress and more precision. Not all shapes are created geometrically equal and how I do it varies.
I true up my blocks and sub-units as I go. Periodically we know specific measurements that I call "justifiers" that is, we know this particular square is cut correctly at 3.5, and so this 9-patch it matches/faces also has to be 3.5. Or that sashing is cut at 12.5x2.5 and so the square it touches has to be 12.5" too.
I keep my pieces as even as I can, and so when I stack/sew them up the weight isn't pulling or stretching. So when you put a row or column together you put two blocks together, and then another 2, alternating amounts but you don't end up with 6 blocks in a strip and adding the 7th.... it would be (2+2)+(2+1). Same thing then when you put the columns/rows together. Keep the weight and sizes as equal as you can.
I find I get the best results when I pin, and for proper pinning that is about every 2 inches. It just is.
Sometimes I'm sewing a bit scant or a bit tight, I'm more concerned with consistency than anything else. By the time it comes to make a border, my top might be 2" bigger or smaller than as designed, I prefer to measure/fit the actual results than the planned. Honestly though, over 100" you can fit in a pretty good sized difference.
When you are actually trimming something like solid border square, it helps to have a nice large square ruler, preferable one bigger than the block. 12-16" is reasonable. Before all the specialty rulers I had a plain large drafters triangle. No measurements but a big right angle was what I was wanting.