First thing is to prep up your fabric and place in your hoop.
Stem stitch is a stitch I use often and love, but I still think it needs more perfecting. For me, I find it is a good idea to start on a scrap piece of fabric and do a few minutes of stitching before actually commencing on my real embroidery piece. This gets me into the swing of the stitch and hopefully gets my stitches more even.
In stem stitch, for left handers, we start to the right of our stitching line and work to the left. You bring your needle up through the fabric, make your first stitch. Next you bring your needle up half way back through and just under your first stitch, then make the stitch the same length as the first, bringing your needle up meeting the end of your first stitch (butting it up as close as you can).