I use masking tape to mark my X's. Reposition it and use several times. You get a perfect X every time.
I also use masking tape when I'm quilting a grid, you can use narrow or wide tape depending on the look you want.

I just wing it on rag quilts..and have had good luck everything always lines up like it is supposed to.

I just eyeball my X's and don't worry if they are off just a smidge or so. When the flannel is washed, it will shrink some and you can't tell that the X's were off.

That is exactly how I do it!!

That is exactly how I do it!!

I do a single line quilting design on my embroidery unit on the machine. There are many hand quilted look designs on the cd's

you know once it is washed no one will even notice if those lines are straight, the idea is to (quilt) the layers together so they do not shift, you do not have to do an x, you can run a wiggly line down in one direction anywhere, then wiggle a line across the other direction, so everything is held. i usually just use a decorative stitch and make it easy; one of the great things about rag quilts as they are fast and easy, you do not need to be so precise as to mark your squares, relax and have some fun with them :)
you can get some really fun great designs when you get creative with raggy quilts, be adventerous, it is the easiest method to experiment. you are still getting practice stitching, but you don't have to (sweat the small stuff) because when it gets washed it will not be noticed!

I just start sewing from one end to the next. I actually told my DGD not to make the lines straight. We did squiggles, wiggles and circles. I wanted her to have fun and not be so hard on herself. It came out great.

I'm with most, I just sew corner to corner, I haven't made a rag quilt but, I did make a 3" blocks and just tried to stay straight and all appear to be. If someone looks that close, then they deserve to find a flaw.

I line up my squares and before I sew them, I take the top square and fold over the opposite corners one at a time and then crease an X on the top fabric piece only. It remains marked long enough for me to sew it, and there is nothing to erase or to stick to the fabric. It works for me.