It might seem a bit obvious, but I've made this mistake more than once.
When you are cutting out stretch fabric, you need to be aware that it can distort.
So if your fabric needs to be laid flat, relaxed AND be supported.
If you let it fall off the side of the table, you may end up cutting your pieces a bit small or wonky.
|You can see the stretch as it falls off the corner!|
You want to make sure that any fabric which does not fit on the table is lifted up so that it isn't pulling. I have a very small table to cut out on, so I need to work piece by piece to ensure the fabric isn't going to distort. I plan things out on the carpet to make the most of my fabric, working from the edge or the corner, but ultimately, I find I have to go piece by piece. Also, if you pin on your pieces and then let them fall off the sides, it is very likely your pieces will tear.
Of course, if you're lucky enough to have a big cutting table, same rule applies - get the extra fabric on the table so the fabric is flat and relaxed.