I wish I remembered where I read this, heard this, saw this...
We all know the trick about making two half-square triangles. Sandwich two squares, right-sides together, draw a diagonal line, and the sew two quarter-inch seams (using the inked line as a guide).
Now comes the trick. Pressing the blocks open.
Normally you cut the unit in half, along the inked line, and press open. But, with the bias seams, those squares can stretch out of shape and get wonky.
Instead, press FIRST...
...and THEN cut them apart.
Pretty nice, eh?