Speedweaving is pretty simple once you get the hang of it.
Be front and center on the lanes, and constantly be aware of which lines are the shortest, and as guests pass the lanes, ask them "Are you ready to checkout?" and if they are, direct them to the quickest lane or call for a backup. If I call for a backup, I will direct the guest to an open lane and flip the light on, and tell the backup responder that I have a guest for them on Lane __. I usually don't hop on and start ringing unless its express and the backup responder is taking a while to get up to the lanes.
Be sure to try and remove speed bumps. Do stuff like moving baskets/carts out of the way, hangers on clothes, etc. And #1..... Be really quick about addressing Help Requests. Nothing kills checkout speed more than a cashier waiting for a GSTL that is taking their time.