Cross hatching can be diagonal lines or squares either straight or on the diagonal or diamonds.
If you are going to do squares on the diagonal which is the most common, I suggest the following. I learned the hard way one time.
Mark every inch all around the quilt or block. then with long straight edge connect the dots from side to side.
Many instructions say to put tape down the center and keep moving the tape or use the guide on the ssewing machine.
what will happen by doing this is that your squares or other shapes will get out of alighnment by the time you get to the edges. Making dots every inch or or whatever measurement you want will make the grids more accurate.