Stiching in the ditch- help!
 

I have an attic window quilt on the frame and have tried to quilt it by stitching in the ditch and can't keep it straight. Since it's on the frame I'm going to baste it then stitch in the ditch on my regular sewing machine. Any ideas on how to stitch in the ditch and keep it straight on a long arm?

a straight line with a long arm is only as straight as you can draw a straight line- unless you use a ruler-
there are special rulers for long arms= and (table/platforms) that fit the machine making the ruler work easier- if you want to do lines straighter than you can (draw) you would need to invest in some (attachments)
don't use a regular ruler you use with your rotory cutter though!!! they are too thin- the foot jumps right on them and breaks needles- causes damage- you need thicker rulers - who ever manufactures your long arm more than likely offers rulers, and other attachments to help with different techniques

The other way to sew a perfectly straight line (horizontal or vertical) with a longarm is to use channel locks.

don't stitch in the ditch, but just off to one side. I find it easier to keep a straight line.

I've used the long edge of a book of checks in a pinch and also the thicker side of an add a quarter inch ruler will work without the hopper foot jumping.

I use a straight ruler for long arms. I was taught to go only the distance of your hand holding the ruler in place, otherwise your cannot control it as well. You move the ruler frequently. It takes some practice. Also, I install an extended base on my Gammill to have a solid surface for the ruler. Hope this makes sense to you.

Stitch in the ditch
 

I saw a demo somewhere and the quilter was using clear "see through" thread. I've never heard of it, but you may want to try looking for some.