It may not be fun, but getting your consistent seam allowance and knowing where it is, is one of the biggest keys to successful quilting.
Funny, Jmoore, my Bernina decided to act up just after I started the Frolic mystery so I've been using my cheapo Brother. I tend to sew scant on the Bernina and apparently I'm sewing fat on the Brother, even chanting "scant seams scant seams" as I go and the seams are right where they should be when I'm expecting to trim. But, in the Brother's defense I use my quilter's foot which is made to give the 1/4" seam from both the left and right side, and it is very accurate on both sides. I'm sort of waiting to get done with the project to take the Bernina in, but the smart thing to do would be to take it in while I'm still busy.
I'm always amazed at people who can switch machines, using one in class and one at home. It's one of my strong sewing superstitions to do all the work on one project on machine.
It can make a difference in your seam allowance, btw, on what threads you are using. For my scrappy quilts with various fabrics and such I don't worry too much and am deliberately using up stable miscellaneous colors of threads from my collection. But back when I was more about precision, that included using the same thread throughout. Back then and on my vintage machines I just used Dual Duty. With my modern machine and modern options I'm happy with Aurifil.
The other thing is your needle. I change my needles a lot, along with rotary blades they are a cheap and easy way to improve your sewing projects and most people just don't do it often enough. I prefer to piece with a 10, I will use a 12.
It probably doesn't matter in reality (my seam is a bigger variable) but I also prefer to use one brand of ruler for a project. I find I cut differently depending on the lines/rulers and there is a slight but noticeable difference if I trim using different squares.