For our quiltalong we need 12 9.5" yellow/black HST. I always add 1" to my desired finished size to see what size I need to start with. That means we are going to have 6 black 10.5 squares and 6 yellow 10.5" squares. (If you are using another color, just sub that for yellow/black).
Step 1: draw a diagonal line across your lighter colored squares. Lay your lighter colored square on top of your darker colored square
Step 2: Sew a seam 1/4" away from both sides of the drawn line.
Step 3: Cut along the drawn line. You can use scissors or a rotary cutter. I use the rotary cutter to save my hands from cramps.
Now I always put my HST LIGHT SIDE DOWN on my ironing board. This ensures the bulk of my seam will go toward my darker fabric. Imagine how ugly it would look to see black fabric peeking through the seams behind white fabric. I then run my iron over the seam. This is called setting the seams. I saw this on Missouri Star Quilt Co. videos and it works. It gives you a very crisp line when you open up your HST. Once your seams are set, you just flip that dark side over and press again. I push the fabric with my iron and let the iron do the work. I don't pull and tug on my HSTs.
Up next, Piecing your zigzag!