I teach FMQ and I don't recommend marking. That's why it is free motion. What I tech my students is how to think your design ahead of time, practice with paper and pencil, or with fabric scraps on the machine with needle but no thread. You see the holes and can see what it will look like. I do recommend to mark straight lines. Otherwise they never come out straight. Others have given great recommendations. No matter what I suggest you test your technique before you do your quilt. Try to do it under the exact same conditions to make sure it will work for you. No technique will work for every fabric every time, so test it before you use it on your quilt.