As an aspiring music creator you are certainly faced with two terms: 'Mastering' and 'Mixdown'. So what is this thing everybody talks so much about?
Imagine a chef, he has a bowl of soup which is a disaster of a meal, but he still has to serve it to his guests. He tries to save the situation by adding some spices, putting something appetising on the top and serving it on fancy plates. This guy won't stay long in the cooking business.
On the other hand he could have put effort in selecting the best ingredients for his soup and carefully cooked them with a lot of love. The result would be a lot better than the first scenario, wouldn't it?
Now to make the ultimate soup, you both have to spend time and love cooking it and know how to make it look as appetising as possible. Consider the first example mastering and the second mixdown. To make a truly good track you have to know how to use both these methods.
No matter how good at mastering you are you can't save a track with a crummy mixdown. Mastering is about making your track sound extra good, and making it sound good whereever it's played: in the club, in your headphones or in the car, etc.
Mixdown is a lot about experience, you learn what frequencies your favourite kick spikes in and so on, you learn just how much compression you can add to a bassline before it sounds totally lifeless and things like this. To me, mixdown is a lot like tetris: it's like planning something on the go. You always have the mixdown in mind when composing your track.
So the best way to improve is to practice, practice and practice. And read the occasional article about musical production.