if you're planning to make your square and cut it in half diagonally, remember that you need to add seam allowances where the stitching will go. in other words, it won't work. you either need to use the drawn line method, which already takes the seam allowance into account, or cut triangles which have been made larger by taking the seam allowances into account from the get-go.
as for staying 1/4' away from the drawn line, just practice a little bit. you just need confidence.