I use an app on my phone called Quilting Calc. It also does borders and bindings estimates.
Before cutting, I will put pins as markers to make sure there is enough fabric. You need to know the amount of extra fabric needed if you use a long-arm quilter.
If the fabric has a large repeat, you will need extra for matching the repeat on the seams.
When I seam the two fabric widths, I make sure the selvage is running on the same side of both pieces. Meaning that it runs on the "left" side of piece # 1 and then on the "left" side of piece # 2. I want the design to run across the two pieces especially for directional prints.
If the selvage is on the "right", it goes on the "right side of both seamed pieces. Hope that helps!