1) Do what you like.
Sounds obvious, right? But for me it was hard to even find out what I like and how to choose. It still is. Right now I feel I do not want to go back to the way I lived my life. This may sound dramatic, but the changes can be little. Hardly noticeable even for someone who is not me. I recently read an article online that said that busy people are people who cannot choose. And I think that's true for a lot of people. I do so much different stuff, I was always behind with administration, studying, contacting people. It's very frustrating.
The first thing you have to do is find out what you want to do, what you like to do. And that's not so easy. Especially as a classical musician. We have all of this tradition, composers, musicians, recordings, concert etiquette. A lot of people choose something they go for because people before them did it successfully. Or play music because it is great music. Sounds like a good reason? It's not! There's so much great music out there, but you have to find music that awakens passion in you. And it might not be Bach, and that's ok. You can listen to Bach, but you don't have to play it because he or she did it and recorded it and it became a huge success. Horowitz is great, the Royal Concertgebouw is as well, but it's not the basis of music, it's a road you can go, but you don't have to.
As a saxophonist I wanted to make my life work out of playing the Creston and Denisow Sonatas with my pianist. And they are great pieces, but in retrospect, I like playing with a pianist, but I love to come up with my own ensembles and experiment, do cross-over. My teacher was Arno Bornkamp and he played those sonatas many times per year with Ivo Janssen. And he was my example. So I wanted to do what he did. But there's so much more. Music is art. Is about creativity. Also as a performer.
2) Take composition classes at the conservatory.
As early as you can, learn to play with notes, make up your own, compose, improvise, even as a classical musician. You never know what is going to happen. My buddy Remy van Kesteren is a composer now, he became one in half a year and recorded a cd for Deutsche Grammaphone with his own music. Reall, you never know. And if you don't do anything with it, it at least gives you insight in the composing process.
I do think that classical musicians should start writing their own notes at least partly. We are influenced by Stravinsky and Bach, we see and hear their notes and know we can't do better. Sure, for most of us this is true. But Stravinsky is not you. We've heard what Bach is about, and it's great, but I would love to hear your contemporary comment on it for example.
I found Spotify, despite the obvious criticism of the medium, to be a great tool to find out what I like to listen to.
3) Don't go with the obvious flow.
A conservatory is called that because it wants to conserve music. So what we learn (and what we should learn!) is the stuff people before us did. Like Creston and Denisov. Learn that stuff and in the mean time think about what you want to do. In the last year of your bachelor I think you can have a basic idea of how you want to spend the coming couple of years. Stick with it, and on the other hand, give yourself time to adapt to new developments:
4) Allow yourself to change.
When students come to the conservatory to inquire about the study., they often say (influenced by their parents) that they might study something more 'useful' first and that after that they can always still study music. I would say it's much more logical to do it the other way around.
Motoric development is very important for conservatory and it's just much more flexible when your around 20.
My point is, after conservatory you do not have to stick with it (despite what I wrote earlier). We all develop. In those four years of study you might find out that you have talents in other areas. Meanwhile you did a study which develops the brain and body in a certain way. You learn to be the ultimate multi-tasker, you have spend numerous hours by yourself and with your instrument in a lonely studio, studying and learning about your music and yourself. It's a form of therapy. Those traits always come in handy at some point in your life.
Also within the music area: you can learn about music theatre and decide you want to pursue that. (See number 5) or maybe you wanted to be a soloist and find out that you are really more of a chamber musician.
But in the end it is very important you finish what you were doing. If possible, finish that bachelor study, study the basics, scales, some traditional pieces, different styles, etcetera. It's never for nothing.
5) Be a sponge.
Absorp as much as you can, not only music, but also fine arts, literature, concerts by others, interact with other people, philosophize, etcetera. Because your music has to be about something. In the end we are story tellers. We need a story to tell, experiences in our life.
This is very important: absorp as much as you can and, especially I the beginning of your studies, do not try to form an opinion just yet. Just listen to what's out there and let your taste develop by itself, without your head telling you what to do and feel.
But you also need to find out what's out there. You don't want to rely on releases by the biggest labels and concerts in the largest concert halls to know what's going on in the music world. There's so much more. There are underground concert halls, musicians who work with music theatre, chamber music in so many forms, ... Find out about initiatives like Splendor (splendoramsterdam.com), zaal 100, OT301, about musicians who go their own way, like Remy van Kesteren, Raaf Hekkema, Ralph van Raat, ...