Caution when ripping. That was they only way we used to cut fabric at the stores, but, back then, we knew the complete and correct fabric content. Only 100% cotton rips clean and even then, some just won't tear right. Do not ever think the cut end is accurate. Fold to match a selvage and have it on a flat surface. It should give you a true 'flatness'. yes, today's selvages can get a bit wonky, but when you put a large section together, most of it will match. I usually give this a light press and then refold it over again (giving the four thicknesses). I clamp the edges and then cut my strips from it. Then I open those more manageable pieces to cut my smaller pieces from. Same principle works for larger pieces for backing. I don't cut those often because I like to do stuff to my backing, so I usually don't use full length pieces (maybe 1/2 length). But, as we have said many, many times, what works for you is the correct way!