Lay your triangle down, dark side up, and press to set the stitches...
Voila! Perfect little half square triangles!
Cut two squares, one light and one dark. Lay them right sides together.
Draw a diagonal line from one corner to the other.
Using a 1/4" foot, sew 1/4 inch from the line on each side.
Trim it right on that line between the stitching and press as described above.
Trim the tags.
Using the 45 degree line on your ruler check for accuracy and trim as needed.
Start as above, with two squares, right sides together. This time sew around all four sides (these will of course be much smaller than the ones from Method #2).
Press and trim tags and you have 4 HST!
There are also some printed papers you can buy from your LQS called Thangles. These can be used to paper piece HST, and are very good for accuracy. Some drawbacks would be that you have to pick off all the paper, and you will have to buy them in the size you need and they would be good for only one use.
**Now for my disclaimer**
The methods above call for you to figure out how big you need to cut your fabric to end up with the HST size that you want. Personally, I live by the "better safe than sorry" philosophy, so I purposely make them a little larger than my pattern calls for and trim them down so they can be perfect. That can be quite a pain if you are making a lot of them! There are pros and cons to each method, but isn't it nice to have options??