"The first topic is about defining your style.  I had one photographer tell me I needed to be more focused (do not remember his exact words).  I was never sure if he meant stick to photographing models, or landscapes, or whatever, or something else.  Also, over the years I have seen work by other photographers that I know, love their work, and then think I should do something like that.  But, then I realize, while I love their work it is not what I like to do.  For me, I like shooting a wide variety of things.  I like shooting people because I like the interaction with them.  However, I also love landscapes, cityscapes, old buildings, wildlife, and probably a few more things (oh, old rusty cars). "

Ok, so when I first got this question my reaction was like "No dude, never change your style on demand, just be you" which is I now realize a very artist (=infantile?) response. So here are my thoughts...

First, you can definitely shoot landscapes and street photography and fashion, and still have your style. In fact, I see a lot of cool fashion editorials that mix up portraiture with still-life either by approaching human body from architectural perspective, or by playing on juxtaposition an object and a subject . Or maybe your style can be all about reflections, or about humor,  or about ambiguity. Subject is not the only variable to define your style.

Another thing is, if you can't define your style, it doesn't mean others can't. I could never define what I do, I think some of my stories are very different from others, like other end of spectrum. Yet people keep generalizing them from "dark romanticism" to "emotional photography" to my style being "very Russian". I guess this happens because 1. people like categories 2. at the end it's just how my vision works, it has it's certain way no matter what story I set up to tell. So as an artist my approach would be "do whatever you want, do it well, and people will define you"

At the same time you need to understand it's an artist's point of view, and putting your own curiosity above all, you unavoidably serve some amount of pictures-to-hate to your viewers. Some will say "oh, well, she is an artist", but others, especially the ones who pay money for your work won't have it, because for them your pictures are tool for their own promotion and their business success depend on it. So the entrepreneurial answer to your question would be, find your clientele and audience and then shoot what they want to see how they want to see it. Have a style to differentiate from other photographers and fit to the aesthetics of your clients-to-be.

So at the end it's up to you: building from inside out and being authentic will give you the best style at the end; building from outside in and adopting to what's hot on the market and what you differentiator is will give you the best return. It doesn't mean that you can't still work with clients in the first case, just try to have returning clients, who trust you won't use their set as a playground too much and will leave your experimentation to personal work. It also doesn't mean you are not an artist you if you are audience-oriented - you are just a bit more Warhol than Van Gogh:)