There was a study showing that women rated men who weren't smiling as most attractive. Now, sociological/survey studies are flawed but this is still interesting to consider. I personally hardly ever smile (more smirking) around women and it's rare for them to them complain or bring it up. The idea that you need to be a bright and cheerful high energy humorous man isn't really accurate. Some women might like that but this is where "being yourself" is actually beneficial. I've always found the ideas of forced smiles to be asinine; if you aren't smiling naturally then just let it be.
Maybe there is such a thing as "tactical" smiling to let show your intentions and get people to open up, but I don't bother with it.