Depends how you are quilting. For hand and DSM quilting I use painters tape. On the DSM after quilting the first line I use a seam guage adaptor for the subsequent lines. For hand, I use my ruler and reposition the tape. For LA I use the chaco liner in white and a cutting ruler.
http://www.amazon.com/s?ie=UTF8&page...Achaco%20liner For dark fabrics. Blue water soluble pen for light.
NOte of caution, have had bad luck with the colored varieties embedding in my thread so I stick with white only.