My top tips for precision piecing are:
1. using a straight stitch needle plate on your machine
2. fine sewing thread - my favourite is Aurifil 50wt
3. a fine sharp needle - I tend to use Schmetz Microtex size 60
These tiny spool blocks measure just 2.5" square, and have been pressed flat on my wool pressing mat, with the seams pressed open to reduce bulk...