Make a small cut into the selvage edge, enough to "expose" the weave or threads. Take one of the threads that runs accross the fabric width and pull it out. Because the thread or fiber is secured at the opposite selvage , it will gather up , you can pull till it breaks pulling out that thread leaving a line, then cut on that line till you reached the point where the thread broke and pull it again. On printed fabrics just pulling a little and working the gather across the fabric will take that printed thread and it will be noticable because that printed thread thread will not be in the same place in the print . If you saw this done once its a whole lot easier than trying to write it to explain.
NOTE: do not use this method on most batiks, way too tightly woven, it will just make you crazy. In this case if a batik is really off grain ... I let er rip! to straighen.