Somewhat Stretchy : Tips

Don't cut corners
- Check measurements lots
- Pin patterns generously to the fabric before cutting through both
Pin patterns to the fabric perpendicular to the border, points towards the border: you can lift the fabric with the pin point to push it through
If you're cutting velvet, fold it back-to-back, so it doesn't 'creep'. Or cut it single-thickness.
My mother told me never to cut paper with scissors used for anything else. Apparently, this is just a clever way to discourage children using the nearest scissors to hand for cutting paper, cardboard, wire, curtains, bricks, or live electricity cables. It's perfectly fine to pin patterns to cloth and cut through both the cloth and the tissue paper. I've also cut through the brown wrapping paper I've been using when creating my own patterns, and the world's not ended as a result. Probably still worth avoiding trying to cut through pins though.
Most of my patterns call for cutting cloth folded in half. I'd find this much easier if I had a wider table: I'm currently using a wallpaper pasting table which is usefully long, but rather less than 30" wide. I'll probably end up buying another wallpaper table and bolting the two together, then finding a way to cover the joins.
To fold the cloth in half, I pick up the first yard roughly where I think the fold should be, and hold it up, adjusting until the machined edges hang freely together. I pin where I'm holding and half way between, then repeat that until I've pinned the whole length. Obviously, the shop-cut edges are almost never square.
I tend to pin pattern pieces starting at the fold and working towards the machined edges. This is mainly because my table's too narrow, but I think it also helps keep it laying flat, and makes it easier to smooth out any wrinkles that appear as a result of pinning.
Dawn always cuts so that the upper blade of the scissors is away from the pattern piece and she can see exactly where the pattern line is in relation to what the scissors are doing. I tend to forget this.
I've marked my scissors' tip to make it easier for me to make the pattern alignment notches.
Dawn showed me how much easier it is to sew two edges together, rather than trying to control three - so if I need to sew three edges, I sew two of them together first.
I still dislike the idea of simply cutting through serged seams, probably based on what happened to the leggings I bought from the Canary Islands. I tend, therefore, not to use the scissors on the serger, and I knot the loose chains at the ends of seams before sewing over them. Dawn's pointed out that knotting the chains is pointless because the lock threads should have the enough slack to match the stretch of the garment, if the machine's tension is set correctly, and hence won't move relative to the fabric, but I still feel better. :) Not using the serger's scissors also means that I'm incorporating the seam allowance into the garment, making it a bit larger and potentially making pieces not fit with each other properly. Once I've unpicked a few more serged seams, I'll probably become comfortable with Dawn's suggestions.