I have two Command hooks inside my shower to hang wet washcloths and two on the tile on the outside of it for wet (or dry) towels. I bought the brushed stainless/nickel look ones like this. They are very, very sturdy and no drilling necessary:

I have Command hooks too--they have a big variety and you don't have to think as hard about the holes. :) Even if you end up drilling, they're great to test placement before you do.

If you will be using chrome hooks (not ceramic tiles with hook shapes) you will want to install them after tiling. This is how we did ours:

We waterproofed the holes for the robe hook we installed in our shower.

The hook sits in the direction of the waterspray, but that's not an issue as we just use it to hold a back-scrubber and a body sponge.

We drilled two holes through the tile and filled them with silicone before inserting the screws. Additionally we applied more silicone under the hook's cover plate (hides the screws) before installing. The tiny set screw faces downward, so we didn't silicone that separately. Done. It's been 8 years, is rock solid and doesn't cause leaking.

I don't think we could have used the Command hooks, as our tiles aren't totally flat, they're full of divots and grooves etc.

Gatco Lattitude robe hook: