Learning level specific movement techniques helps give you more options. More options to choose from = less predictable. If you can combine that with certain character specific spacing tricks in regards to the platforms, then you should be good to go.
Alot of the time people are moving around carelessly, putting in noticeable effort to be "random". The more you think about trying to be not predictable, the more predictable you become. I find it alot easier to break habits if you focus on other things. Worry about your positioning and why you are where you are. Is there a purpose for why you are in the air? In there a purpose for you being this close to your opponent? Why? If you can't figure it out, then its most likely a bad habit. Try not to get discouraged though, because there are a lot of things you can't do anything about in this game. Tech-chase scenarios are the first that come to mind. It might seem like you're predictable because Marth chases you all over FD. But thats how the match-up works. The level is flat and he has a long DD, its really not all that hard to do. I think a major step is knowing whats in your control to change. From there its just isolating those parts of your game, figuring out why you didn't do the best option, and do it.
Your movement will naturally align itself and contemplating the matter won't be necessary - because as a player you will (or should) adapt accordingly and move in response to your opponent's decisions.
Stay on them and just play your game. If you're making bad tech options or jumping into things. Examine your choices in those situations after the match. Did you jump because you felt pressured? Because you were close to the edge? How could you have avoided being hit? How could you have avoided that entire situation? Self-improvement is hard, I know. You need to learn to question yourself and the things you do before you can make changes to your game that make any sense.
In short, play based on reaction, and try your best to make you decisions based on what your opponent is doing.