I have a Janome 6600. When I am sewing things where it is not crucial for have a perfect 1/4 inch I use Connecting Threads and have the machine set on 3.5. When I am sewing something that is very important for the scant, I use Aurifil thread and set the stitch on 4.0. I will press open if there are many different seams.
Each machine will have a different setting but practiced many times to get mine the way it should be. I also slow down my stitching when I want to be precise and am very careful not to let the seam veer off at the very end.