Just Get It Done Quilts (Karen Brown) has a video with a number of easy beginner-friendly quilting ideas using a domestic machine:
https://m.youtube.com/watch?v=2Uv5rCcvH4U
My favorite is the big swooping wave - you only have to mark one wavy line and all the others echo that line more or less. I'm terrible at free motion quilting so I love that this design is curvy but uses a walking foot so the stitches stay uniform.