This is the music of your time, and it is yours. You have the power to influence it through interaction with composers. You can change a composer’s entire approach to your instrument or understanding of it. One of the most crucial aspects to a developing composer (myself very included) is performer feedback.
You will face new challenges that will take you out of your comfort zone. This is essential for learning!
Be a well-rounded musician; play a variety of styles/eras and be able to tackle anything
There will be gigs for playing new music. Developing experience here will make you a better candidate for these opportunities.
Playing new music is networking. When you give a positive performance of a composer’s work, other composer notice. Be someone many composers want to work with. (Years from now, this could lead to a concerto written specifically for you!)
Treat rehearsals of new music as seriously as you would an orchestra rehearsal. Show up prepared, early, and ready to create music. (Composers will really appreciate this, so much!)
Rhythm, rhythm, rhythm! Tricky rhythms, especially for ensemble playing, need to be learned well. Pull out your metronome.
Like an etude or orchestral excerpt, start off slowly and focus on some challenging spots. If a recording is available listen to it. If you can get a score look over it.
All music is expressive. Always maintain good sound quality and tell a story, capture your audience. As composer Libby Larsen would say, verbatim, "Get off the page, or get off the stage!"