Is clay always on the surface?
Is it underwater?
Do I have to dig to find it?
Is it in the bottom of the ocean?
Is it closer to sea level, below or above?

I just recently posted this in another topic as a reply, but this is just to clarify to most people that there is most likely clay in your seed, you just have to know where to look. So here it is. Clay ONLY forms with Sand usually with that sand by or surrounded by water. Clay can only be found along the diagonal line that splits the map from the north-west corner, to the south east corner. So look along that line for any sand, and pray. Clay rarely will be found deeper than three layers, so if you start hitting Sandstone or Cobblestone, you won't find Clay there. In the few seeds people found sand, it was usually on the surface, at the same level as the water. Clay looks like grayish Sand, so look for that. The Tutorial seed has clay at the North-western most sandbar, so you can use it to help you learn how to distinguish clay from other blocks, and see how deep to dig. It's right at the surface.