If it's a place you can be in, you use "in". If you can't be in it, you can be "at" it. Though otherwise, the difference is not very well defined.

IN MY PLACE -"Will you go to the meeting in my place?" = will you represent me/go instead of me? - "I am sitting in my place at the table" = I'm where I should be/in the seat that has been reserved for me/where I always sit. AT MY PLACE -"Let's all meet at my place at 6.30pm" = at my house