I'm a newbie quilter, but a long time sewer and there are a couple of carry over sewing tips I've never seen mentioned.
1) If you have to pin, don't hold the pieces up in your hand and jab a pin in. Lay them on your work surface, line up the edges and, slide the pin in so it's as parallel to your work surface as possible. Another way to explain is if you dropped the pin on the fabric and just pushed it in. If you hold up the fabric and just stick the pin in, you can actually move the fabric around. There are times when you can't lay the pieces down, but if you can, try this and see if it helps your accuracy, especially with small pieces.
2) when I put binding on, I sew it to the front, then press it 3 times around. Once to set the seam, once to flatten it out over the edge and then I actually fold it over and press it. It takes a few min, but it really, really, really helps, whether you are hand stitching or machine stitching to finish. I don't fold over and iron the corners, just deal with them as you come to them. If you use bias binding, remember to press, not iron.
Don't know if this will help anyone, but thought I'd post.
Nancy