Strips for most projects are cut cross grain (from selvedge to selvedge). These strips are a convenient length (42"/44") to use in your piecing.
The lengthwise grain has less stretch and is sometimes used for vertical (up and down) sashing and border strips.
Strips need to be cut straight
If the fold of the fabric is visible, cut at right angles to the fold. It's OK if the selvedges do not line up.
If the fold is no longer visible, fold the fabric in half with the selvedges together. Lay the fabric down and slide the top layer to one side until the fabric lays flat.
Straighten the fabric by cutting it at right angles to the fold.
do this by placing a cross line on a ruler on the fold, and then rotary cutting the fabric.
The shorter the distance to rotary cut, the easier it is to cut accurately; so after straightening the fabric, fold the fabric in fourths and cut strips, lining up a ruler with the folded edge.
I like to undo one fold of the fabric and re-straighten the edge after cutting five or six strips. Then refold, restraighten, and continue cutting strips.
After a strip is cut, do an accuracy check.
Accuracy Tip: Fold the cut strip in half, end to end. Is the strip the same width at both ends and at the center of the strip?
Straighten the strip or strip set
Before cutting squares or rectangles, trim the end of the strip or strip set to straighten and remove the selvedge.
If you are cutting the strips or strip sets for diamonds, don't bother to straighten the ends.
Right handed quilters, trim on the far right side.
Left handed quilters, trim on the far left side.