As close to the middle of the chart as I can! I like the it is easy to find the middle of my fabric and knowing that correlates to the middle of the pattern. When starting my first HADE, measuring to find the top left corner of my fabric was a nightmare for my brain!
I always tend to start at the top right, then I go with the different parts of the picture. But, if its inside a sqare or some other kind of form, I start with the picture onli, and left the form for the end :)
For full coverage I usually start in a corner and work horizontally. For more simple patterns I start in the middle and work my way out, starting with the color closest to the meeting points of the arrows that show where the middle is