Personal style develops as you grow and change. In the years we are in elementary school, middle school, and even high school, our style is influenced by society, by our surroundings, and by our friends. At some point, individuals find a style that suits them, and that they feel comfortable in. It doesn’t matter when that happens, it only matters that it does. Naturally, as we grow and develop and move closer to discovering what our personal style really is, we look back on past phases and can be quite shocked by what we used to wear. (Change “shocked” for “horrified” or “amused” if either fits better.)
Trends make the whole personal style thing a whole lot harder. It's expected that you keep up with trends, but it's also expected that you concurrently maintain your own style. How is that stylistically possible? By adapting to every trend that waltzes down the runway, you are, undoubtedly, compromising your style. So I guess, in my opinion, doing both is impossible. Or rather, doing both fully and to the utmost extent is impossible. My advice would be to use the trends to find your style- what you like, what you feel comfortable in, what makes you feel like you- and then once you find that style, only follow the trends that fit those three W's.
The people around you as well as your life situation will always affect your style in some way, but don't let them change it completely. Remember, your style is an outward expression of who you are as a person. Own it.