W = Writing. There really could only be one answer to "W". And it is true the more you write, the better you become. It also pays to vary the type of writing you do. I don't believe in writers' block but I DO believe in writers having "off" days when the words simply won't flow as much or as easily as you would like. We're human after all. What I have always found is that if, say, a story is not working out right, if I can go on to write something else. such as my blog post for the Association of Christian Writers, then that will be fine. I am never stuck on ALL writing. Usually I find as well when working on something else the solution to my original problem comes to me.
X = X-Rated. Definitely not for me but the fiction market covers all kinds and most tastes so there will be something in this department! The same rules apply to this kind of fiction too. You still need fully rounded characters. You still need a plot. You still need to know who your readers are likely to be and to be able to reach them.
Y = Young Adult. There are many fine novels in this category and many are read by adults of all ages (and why not?). I would say my From Light to Dark and Back Again could be read by this group. Yes, there are many YA novels that deal with issues but there are plenty that are straight entertainment and cover practically every genre.
Z = Zero Heroes. Am I cheating here? Maybe! What I mean by Zero Heroes are those stories (of all lengths) where the hero isn't particularly likeable but is by far better than any of the other characters and you root for them to do well. Sometimes a quest can be the making of them and they turn out to have hidden depths.