Wash and iron your fabric. If your fabric runs, be sure to wash it with like colors. I sometimes just run the washer with minimal soap, or soak the fabric in a hot tub and place in the dryer. If you want to color test a fabric first, just cut a piece and toss it hot water. If it runs, I would use laundry soap.
Here we dissect the parts of the fabric. You want to fold it so the selvages meet. When you get your fabric cut at the fabric store, they are cutting the raw edge of the fabric. This is the part we will even up and cut off to cut strips from. Some stores tear right down this grain after making a snip in it. Amazingly, it tears straight! The other labels are for your reference.
The ‘bias’ has the most stretch in fabric. Test it for yourself. Which part has the least stretch? Lengthwise or Crosswise? Can you figure it out?
Line up the fabric on your cutting mat. Make sure it’s ironed! This photo looks a bit wrinkly, but it was smooth enough to cut straight.
Fold up to meet the other end. Line up the bottom crease nice and smooth on a horizontal line and allow just the uneven edge to cross over a vertical line so you can cut it off.
Using the ruler and rotary cutter, line up the ruler along the uneven edge, press gently but firmly and cut the edge off.
Slide your hand up and along the ruler as you cut (lift and slide don’t move the ruler!) to keep things straight. Your fabric is ready to cut strips.