With my vision issues and my scrappy style of quilting, I can't see most lines. For fancier designs I've spent a lot of time stitching through paper. I've tried tissue paper and newsprint, but now I buy rolls of cheap parchment paper from the dollar store. The roll is 1 foot wide by 10-12 feet long. I will either draw or buy a pantograph for my base design and then with the parchment paper on top, I simply copy the design with pencil. Warning: If you are quilting with white thread there is a small chance the graphite will rub off and be almost impossible to get out of the thread so I do not recommend with white thread on a white background.
I can freehand basic meandering designs, adding in motifs like stars or flowers or loops or whatever. I do have to keep on top of myself to keep spacing consistent and not quilt myself into corners... Typically with my queen sized projects I do pretty simple designs in the body of the quilt, and then maybe something a bit more intricate on the borders.
For basic functional use blanket quilts like my donation projects and ones I know will be washed a lot, I do a some sort of simple grid but use a serpentine stitch.