I like to use my mat when layering because it’s sticky and it has lines on it. I can line the vinyl up with the lines running vertically and horizontally on my mat.
When layering using this method, you can pick up more than one color of vinyl at a time. The trick is to trim the carrier sheets close so you can put two colors on the mat together.
You can also use the parchment paper hack for applying transfer tape to the vinyl. This is especially great when working with really large designs as locating the transfer tape straight can be tricky.