Visualisation... sounds kinda intuitive, no? You close your eyes and imagine yourself performing the task at hand whether it be scoring a try or crossing the finish line first, but there's more to it than that. A dictionary will tell you that visualisation is the act of using mental imagery to create visions of 1) what you want to achieve and 2) how you want to achieve it.
For me, step 2 was missing for most of my life as I would only picture myself achieving the final result but not the journey to get there and that's as important if not more so than the end result. To this, I would add that, the richer the picture the more effective the process. Think about it using this really simple example. If I ask you to draw a cat and you draw this:
You're not thinking much about the cat other than making sure it doesn't look like another kind of animal. It's simple and it gets you the result you want... as long as you're playing Pictionary and all you want is to convey an idea of a cat. Think of it as the What in that dictionary definition.
Enter exhibit b)
In this case you thought not only about the shape, but the size, the surrounding environment, the movement. How does the cat look as she approaches the jump? In which way do the legs move? What muscles are pushing her up in the air? You even have to imagine what the tiger may be looking at and "visualize" it through your own eyes. Takes a lot more time and effort both inside your head as it does in getting the drawing right, but it looks a lot better and I bet the result would leave you a lot more satisfied too. This is the How, and that is what gets you there in the end.
Sports are like that as well. Olympic heptathlete Jessica Ennis-Hill was well known for using mental imagery to perfect her technique as well as working tirelessly in pursuit of perfection. Her philosophy was simple. If she could see herself executing perfectly in her head, it would have an impact on her physical performance, and it did. It's the process that counts, and when you marry that with the hard work, the result will follow.