I use the Eleanor Burns method, too, and it works very well...you might want to buy one of her rulers, if you're planning to make a lot of flying geese (which also play a part in many pieced blocks).
When you're sewing, rather than stitching ON your drawn line, stitch a little bit to the outside of the line. The seam and fold take up some space when you press the triangle out, and this makes allowance for it.
If you don't have a flying geese ruler (such as E. Burns type), make a template out of plastic the final size of your goose unit. Include (and draw) the four outer seam allowances, and draw in the center triangle "goose". Once you've stitched and pressed your unit, line the template lines up with the "goose" of your unit, and trim off any bits that stick out beyond the template. This will give you more uniform results.
Go easy when pressing the corner triangles -- it's easy to stretch things out of shape. If you STARCH YOUR FABRIC BEFORE CUTTING, you will find your pieces and units much more cooperative! (this is my #1 tip for all quilt piecing dilemmas)