When preparing a small quilt sandwich (top, batting, backing), smooth it out, then press it lightly with a low steam setting and pin it. This prevents wrinkles on the bottom and it holds together quite nicely for quilting.
Why toss out a decent towel -- Serge edges to extend the life.
Use a bias bar to smooth out pillow corners when turned inside out.
Stuff pillow corners with batting to eliminate flat corners.
When storing quilts, refold them periodically. The folds falling in different places prevent them from causing permanent marks on the quilt.
If you are not sure your sewing will be accurate, baste it first on the machine, If it looks good, then sew over it with a smaller stitch to secure the seam.
Leftover fabric after sewing your quilt? Make a matching pillow.
When squaring up fabric, turn the cutting mat instead of the fabric to avoid shifting for accuracy.