First and foremost is to have a white background (can have others for certain categories such as gaming, etc.), your product needs to cover at least 85% of the area, should give customers a clear idea of what they can expect, the minimum resolution should be 1000×1000, recommended is 2000×2000, ratio, as suggested by resolution, needs to be 1:1, although for gaming (and certain other categories) this can be 3:2 or 2:3.
