Masking tape will work, as long as you don't leave it on your quilt top for longer than it takes to sew and the room is not overly warm (like in summer, it may leave traces of the adhesive). You can reuse it several times, too :D:D:D
Once I get a straight line from the tape, I just follow the lines with my guide. Then I use the tape in the opposite direction and then only my guide after that.