Oh my goodness.
I had no idea how much random sewing detail is moving around in this head. When will this series actually stop?
We will see.
I know I promised marking, a huge topic, but some excellent comments have reminded me of fabric pre-treating issues and something old school called "straightening" the grain, which you probably shouldn't be exposed to but I am going to do anyway.
First pre-treating fabric.
This means, more or less, getting the shrinkage out of the fabric before you cut so you won't get your heart broken by bad surprises after the first wash.
The rule of thumb to do what you will do to the garment to the fabric before you cut.
This means if you don't sort your colours and throw all your clothes in a hot dryer you might as well find out before you start sewing if your fabric can cope with that lifestyle future. If, on the other hand, you wash everything in cool to warm water only and always line dry, either outside in a good stiff Nova Scotia breeze (do you know fog takes stains out?) or down the basement on a long line demonstrating that no one is going to ever Pin your family room, do that to the yardage too.
One word about knits though.
All most all knits have the degree of greatest stretch running crossways so if you fold you piece over the line (or shower rod I do that too in the downstairs bathroom) crossways, the weight of the fabric will stretch the knit out starting at this fold, and you will be dealing with wonky from then on in.
Try, if you can, to hang a knit lengthwise along the direction of less stretch.
I always, always pre-wash all knit before I evaluate them - so often they are stretched as they are wound onto the bolt and they definitely need a chance to recover from that. If I have time I even lay a knit out on the cutting table overnight so it can retract/recover before I cut, can make a difference.
For 100% cotton fabrics of all kinds I would actually pre-treat twice to get as much of the shrinkage out of the fabric as I can - cottons, particularly loosely woven ones or twills like denims, can lose as much as a few inches per yard in shrinking - over more than one wash.
For fabrics that you will dry clean, although for environmental and health reasons there is less of that happening these days, many folks are spot cleaning when they can instead, you still should pre-treat.
For wools, the largest category of fabrics like this, you would traditionally do something called a London shrink.
Translated into domestic application this means laying a wet sheet over the fabric, folding it up, putting it in a plastic garbage bag and waiting a number of days for the wool to absorb the moisture and pull in a bit.
You can of course achieve a similar effect with steam pressing, holding the iron over, not on, the fabric and shooting it with steam, but doing that over 6 yards of 60" gabardine with a domestic iron is more than I can stand, although stronger women can and should.
My own method for sanely pre-treating wool is to run a tricot slip or something that picks up very little water through the rinse/spin cycle of the washing machine then put that damp item in the dryer with the wool. Ten minutes on a low heat will shrink the wool just enough without changing it perceptively.
When you remove the wool from the dryer lay it out onto the cutting table to cool right away though, so it doesn't pick up wrinkles.
Now back to fabric straightening.
In the old days when I was a junior sewer my mother made me hold one end of the fabric and pull on it diagonally while she pulled on the other end - this was supposed to "straighten" the grain, although even at eight years old I could figure out that surely would not be a permanent solution. The idea was that the selvage edges would of course be on grain but the cut ends, and maybe the fabric itself, might not be true cross grain.
I can't quite figure out how you can weave a fabric with the cross grain not perpendicular to the selvages unless you were producing some A1 crummy fabric that no one should have been sewing with anyway, but the point about uneven cut ends is a good one.
I am sure if I ever worked in a fabric store I would not be doing exactly cross the grain cuts at all at the cutting table. So it is not unexpected for the cut edges not to match when you fold the fabric in half before you cut. This is not the end of the world if you can recut them with a straight edge, but to make sure all four sides of your fabric piece are entirely on grain you can, if you want, follow a cross thread right across and cut along it.
The way to do this is to make a small cut through the selvage and fray it a bit until you find a cross thread in the fabric. Once you have found it pull carefully along that thread (it may break and you will have to really look closely to find it again) right through to the other selvage. This will make a sort of puckery line along the fabric you can cut along to ensure you are in fact working with fabric that is as much on grain crosswise as lengthwise.
I always do this to each cut end if the fabric is really worth it to me and have never thought that it was not worth the trouble.
Marking will really be next up.