I want to begin by saying that I learned to gather  at young age from my mother, pattern instructions, and sewing books.  They all  suggested a scant 5/8 " line of long stitches followed by another 3/8" line of  stitching.  I could never understand why I was stitching next to the seamline.   Then, it was always difficult to remove the gathering stitches that got caught  in the seam. 
Instead of the method just described, I use a  1/2 " line of large stitches from the edge and another 1/4" inch in from the  first line.  This way the seam stiched at 5/8" will be in between the two  gathered lines of stiching.  For beginning readers, you leave a nice long end to  the thread after each line of stitching. Then you pull the two ends to tighten  the stitchese which gathers the fabric together. I like to pull from both ends  until I get the intended length and arrange my gathers evenly in between.
When I am finished, I  can easily remove the gathering thread.  In addition, I have been using this  great tip.
It came from a tutorial I found on another blog.   I wish could remember which one, so I could give proper credit where it is due.   If I can find it, I will let you know.  By anchoring the thread on your pin, you  can distribute the gathers evenly without losing any on the end.  
Finally, this pattern was wonderful in the fact  that it was simple and had no zipper closing.  However, I did make a change to  the way that I attached the casings for the tie closure at the top.  The pattern  instructions suggested sewing the front to the gathers and spreading the seam to  reveal the stitching,  then stitching over the seamline.  Next, you were to trim  the excess edge close to the stitching.  I assumed this was similar to stitching  in the ditch.  I understood that, but couldn't understand why I would trim close  to the stitching and leave a raw edge.  Thus, I chose to fold the casing in  half,  stitch it to the right side of the the gathers, and serge the edge.  This  is how it looked.  I liked the way it laid, and it will not ravel.