First to remember...the thread has to be large enough for you to really see it.
So, use perle size 8 if you have some...my favorite. Or, if you prefer to use stranded floss, three stands is my recommendation for stem stitch so you'll get nice and plump "S" shapes.
Stem stitch is ALWAYS stitched from left to right, and the thread should be below the needle.
Now, having said that...and you do need to keep that "chant" in your head as you stitch..."left to right, thread below the needle".
But, if you stitch towards you or away from you...then your thread will "appear" to be either right or left...however, IF you get confused...turn your work so that it is positioned where you will be stitching left to right...and the thread is below the needle. Now, rotate your hoop as you need to stitch away or towards you...as you are comfortable with...NOTE which direction the thread is pointing...it will change from BELOW because you rotated your hoop. BUT, it really is still "below" in terms of creating the shape. Just note this and keep going. (If this is confusing...just don't ever rotate your hoop! Hugs!)
Okay, let's begin stitching. Thread your needle and knot the end (or start somewhere outside your stitching area with an anchor stitch, and rework that end under your thread later on).
I'm stitching on my trellis gate design...
Needle up at the beginning of your drawn line...far left point.
Needle down to the right of where you started...I like to have about 1/16th of an inch of space between my Needle Up and Needle Down positions to start. Pull the thread to the back for this first little half-stitch.
Another note: If you have trouble making uniform sized stitches...take a piece of scrap fabric, fold it once to make it double...use your sewing machine to stitch a straight line. Now, use those same holes to practice your stem stitch in...just sew over the machine thread.