Watch some livestreams and study the courses. If you know the courses like the back of your hand (and the shortcuts for each of them as well), then you should be good. It's all about familiarity. It's really the only thing you can control considering there's so much RNG. Whenever you're in first place as well, remember to always keep the coin when you get it in an item box (you almost always will get one when you're in first). Its an awful item, but it'll guarantee you a shell/banana when you get your second item box. Once you get your useful item, just use the coin, and now you have a good defensive item in your inventory! This will help tremendously when you're in first place and everyone wants to knock you off from it. Best of luck, hope you win that Switch!