Batter boards should be placed about a foot and a half away on both sides from the corner.
Make sure the top of the boards (height) are the same on all four corners. I did this by site. I guess you could use a string level or transit.
I have seen several comments about having trouble keeping the overall dimensions when they adjust for diagonal. You must move both strings the same distance. ??? Mine was 24x50 and both 24 and 50 were dead on but the diagonal dimension was off around 8". I moved both lines on the left sidedown around 4". I was then with about an inch. Couple more slight adjustments and it was exact. The 50' distance never changed because if I moved one line a 1/4 inch then the other line was moved the same distance.