I do trays all the time. Find a nice platter with an edge (I use plastic ones that my customers can throw away) and lean them on the back edge and arrange them. Some of the things I try to do is to separate colors and styles to make the platter look uniform. I also make sure I cover up the whole tray so it looks full. I use doilies under them to keep the cookies from slipping and then it makes the half empty tray look nicer as they're eaten. Let me know if this helps!