On a recent picture posting of my "Pastel Minis" I replied to a fellow quilter who was thinking about sewing smaller with the follwing advice.
Use starch. I use StaFlo reconstituted in a 2:1 ratio of water to liquid starch. Pour into a spray bottle and you are ready to go at a cheap price. If after some time the sprayer won't spray, rinse the assembly with warm water to krinse out the dried starch buildup.
One of the things I've learned is to be precise in cutting. I love the narrow black lines on Creative Grids rulers with the non slip backing. I have the 2 1/2, 3 1/2, and 4 1/2" sizes.
Precise stitching is also important. I became even more accurate in sewing when I began using a 1/4 inch foot.
And if it doesn't line up perfectly. Well you can rip and re sew (I will only do that 2 times if at all) or you can just say as my son who was 4 at the time told me "Nobody's perfect, 'cept God."
Good luck in sewing smaller!