I FMQ quite a bit. I only have one ruler. It has a gap in the middle that your foot fits into and allows you to make a straight line easily. Interestingly with FMQ, making straight lines is the hardest part for many people. Learning how to do a meander and other simple FMQ designs is fundamental. Don't neglect those to concentrate on ruler work. I also do stitch in the ditch with FMQ. Matching the thread or using invisible thread. That gives you a lot of FMQ practice that most people won't see and its quicker than using a walking foot.