Stem stitch is a great workhorse stitch for embroidery. It makes a lovely straight line that has interesting texture but is quite simple to stitch. It is the only stitch that I used in my Anatomical Leg Embroidery.
The stem stitch demo above is shown very loose and with the angle of the stitch exaggerated for illustrative purposes. Note that, although there is an angle to the right-to-left portion of the stitch, the line as a whole is straight.
This example is more illustrative of what you will want your finished stitches to look like. They are smaller (more appropriately sized for the size of the floss) and tighter. In this instance, the right-to-left portion of the stitch was stitched horizontally, with no angle. However, making sure that the thread is always below the needle gives the appearance of angled stitches.