I have always started in the middle, as that is how I was taught. However, I have noticed that when my friend starts in the top left, she can preserve a lot of fabric in the end.
I try to hold the rule "move against half stitches move". I like to make half stitches from left bottom to right top, so I start the chart from right top. To stitch from empty to filled. It feels strange because natural for us is while stitching to move as a book reading move.