squaring fabric-newbie

I am trying to make a rod curtain (but with a rod at the top and bottom)and cant figure out how to square the fabric. It is a larger floral print and thicker fabric so it can't be seen through. Can anyone help? New to sewing.

Hopefully I can make this make sense using words

line both selvages up together holding it out in front of you.  Then look at how it drapes.  If it's not hanging smoothly shift the selvage closest to you to the right or left until it does.  I then lay it down on my cutting mat, folding the selvages to the fold so you end up with 4 layers.  Then I line my ruler up with the fold and trim of the uneven edge.

There's also a way you can pull a thread from the lowest point on the cut edge and slowly work it out and you can then cut on the line it makes.

I don't know if that makes sense to you - it would be way easier to see it done.  Maybe there's a YouTube clip...

Pulling the thread never works for me....maybe I use fabrics that are too tightly woven for this technique.  It seems like it should be so easy!

The other technique does work for me with cuts of fabric that are not too large.  Does anyone have other suggestions?  I like to sew garments and think I could improve the way garments "hang" if I could master this initial task.

Can I shed some light on the pulling the thread technique?
Snip the fabric at the selvege edge near the top of the fabric.  Pull 2 threads gently. Don't try to pull it all out in one go. If your fabric has a pattern, just pull it enough to shift the colours out of line and then cut along that small section. Next pick up those threads again and pull some more and repeat till you get to the other side.  If you accidently cut off the threads, just open up the cut and pull the shortest ones in the gap. If you end up a couple of threads out, it won't make any difference to the end result.  YES, things will hang much more nicely if you square off like this.  BEWARE!!!  You may get a fabric that has a PRINTED pattern but it has been printed on the bolt crookedly. (usually cheap ones) If it has a geometric pattern, no amount of pulling threads is going to help this look good, so you may need to rethink if you want to make a garment from this.  good luck