I took a machine quilting class, and the teacher suggested taping a safety pin to the back of the machine in two places -- where the spool would normally sit and then closer to the needle. The hole in the "wrong" end of the pin becomes your thread guide. Just tape the pin so that the hole is above the body of the machine and run the invisible thread through the hole in the safety pin, rather than using the thread quides on the machine. This keeps the thread from slipping off the thread guides, and it reduces stretching. Also, if your thread is on a cone, use one of those cone nets to help the thread come off the cone smoothly.