this is what works for ME - your mileage may vary.
1. when I paper piece and actually stitch through the paper, I reduce my stitch to about 1 on the machine. However, I actually prefer to use the fold-and-stitch method, where I fold the paper out of the way and stitch right next to it. This way I don't have to tear the paper off when I'm done. When I use this method, I don't reduce my stitch length.
2. If the fabric on the back bunches up, I get out a magnifying class and carefully unpick. This is another reason I prefer to use the fold-and-stitch method of paper piecing.
3. I don't backstitch or reduce my stitch length at the beginning or end. That's too much work for me to do on every seam, and I've never had a problem with seams coming undone. However, having said that, when my top is complete, I DO make sure the seams around the edge of the quilt top are secure.
4. 90% of the time I don't pin. I nest my seams, and I also have a tendency to make small blocks, so I just hold it together with my fingers. If I was making a larger block, like 14", I might pin.