Half-square triangles are one of the most commonly used components of pieced quilt patterns.  You can find them in such blocks as Broken Dishes, Friendship Star, Shoo Fly, and Cake Stand, just to name a few.

Triangles can be tricky to work with, so I've compiled a few tips to help you make half-square triangles faster and easier.  

Do the Math:

The magic number for half-square triangles is 7/8.  Simply add 7/8 of an inch to the desired FINISHED SIZE of your half-square triangle.  For example, if I want a 2" finished size half-square triangle, I will cut two squares (one from each color) that measure 2-7/8" each.  There are two methods that you can use to construct your half-square triangles from squares.  Either way, you'll end up with two half-square triangles.

Method 1 - Cut Then Sew:  With your rotary cutter and ruler, slice each square from corner to corner to make two triangles of each color.  Layer color 1 on color 2 with right sides together and stitch a 1/4" seam along the long side.  Repeat with the second pair of triangles.  Press seam toward the darker fabric and trim points.  You now have two half-square triangles that measure 2-1/2" on all sides.  They will measure 2" when sewn into the block and then into the quilt.  This method works fine, but you do have to handle stretchy bias edges.  If you use this method and your half-square triangles turn out to be not exactly the right size, you might want to give Method 2 (below) a try.

Method 2 - Sew Then Cut:  With a pencil and ruler, draw a line on the wrong side of the light color square.  With right sides together, layer the lighter square on the darker square and stitch a 1/4" seam on BOTH SIDES of the drawn line.  Cut apart on the drawn line and press seam allowances toward the darker fabric.  Trim points and you are done. You now have two half-square triangles that measure 2-1/2" on all sides.  They will measure 2" when sewn into the block and then into the quilt.  This method lets you avoid handling the bias edges, therefore yielding half-square triangles that are more accurate in size.

Grid and Bear It:

If you've got lots of half-square triangles to make, then you might want to use the grid method.  This method allows you to make multiple half-square triangles in less time.  There are two methods to accomplish the grid method and one is a bit more precise than the other.  

Method 1 - Gridded Fabric:  This method involves marking a grid on the wrong side of one of the fabrics that you'll be using in your half-square triangles.  I'll use a 2" finished size for our example.  Cut a 8" x 12.5" rectangle from each of the two fabrics that you will be using for your half-square triangles.  With a ruler and a pencil (or your favorite marking method), draw a line 1" from the left short side.  Draw another line exactly 2-7/8" from the first line.  Continue until  five vertical lines are drawn.  Next, draw a line 1" from the bottom (long) side.  Draw another line exactly 2-7/8" from the first line.  Draw one more line 2-7/8" from the second one and your grid is completed.  Now draw diagonal lines through each square as shown below.  With right sides together, layer the marked fabric on the unmarked fabric.  Stitch a 1/4" seam on both sides of each diagonal line as shown below.  Using your rotary cutter and a ruler, cut apart on the drawn lines.  Press the seam allowances toward the darker fabric and trim points.  You will have sixteen half-square triangles!

Method 2 - Gridded Paper:  The gridded paper method is faster than the gridded fabric method because it eliminates the marking step.  It is also more accurate because you don't have to worry that your ruler or fabric slipped during the marking process, resulting in half-square triangles that are not quite the right size.  Here is how it works.  Cut two pieces of fabric to the specified size and place them right sides together.  Place the gridded paper on top of the fabric and pin in place.  Hold the paper and fabric up to a light to see if you've covered all of the grid and make any adjustments that are needed.  With the paper side up and using a very short stitch length setting on your sewing machine, sew on the dashed lines.  Using your rotary cutter (you can reuse a dull blade for this) and a ruler, cut apart on all of the solid lines.  Carefully remove the paper from the back of each unit.  Press seam allowance toward the darker fabric and trim points.

Here are links to gridded paper from BlockCentral.com that you can print out and use now!:

1" Gridded Paper - Finishes to 1" and each sheet makes 24 half-square triangles.

2" Gridded Paper - Finishes to 2" and each sheet makes 12 half-square triangles.

3" Gridded Paper - Finishes to 3" and each sheet makes 8 half-square triangles.

4" Gridded Paper - Finishes to 4" and each sheet makes 4 half-square triangles.