Welcome to Gaia! ::

One of the best things I do is watch videos with tutorials on certain aspects of my instrument that I need help with, or tutorials on things I'm good at already but just to see a different possible way of doing it so I can see what works best. I watch a lot of videos in my spare time from experts or professionals and I think it really helps. Also, just listening to a piece you're working on from a professional recording might help you on interpretation.

(I'm a singer.)

I take classes in French (unfortunately the only language my school offers, I'd love to do more) and always make sure I can translate or get a translation of my text. I've got a couple of different language dictionaries to do this word for word when I have the time as I find this the most helpful, but if not then I'll find a translation online.
Tomorrow I'll be starting pilates classes to help improve my core muscles to support my voice.
Probably an obvious one, but I try and get as much performance experience as possible =P
I haven't found a local drama group that is ran at a time that I'm free but I took theatre studies and performing arts last year to improve my acting and try and remember things like this.
Having an extra practise session infront of a mirror where I focus on expressions and body movement instead of what it sounds like is also useful.
Of course, I also do all the theoretical side of music too, having a deeper understanding of the notes on the page is always good.
OH and I practise & teach piano... maybe not what you're thinking of but having a second instrument gives you a wider understanding of music I believe, or at least it has for me.

I am a big fan of talking to other musicians about music; most of the time it’s about performances, instruments and musician ship tips. I also watch many performances both live and recorded. I find that this allows me to see what the musician does during the performances, like resting positions, expressions, and naturally what they actually look like while playing or singing. I listen to many recordings of different styles; I also find that abstract art is helpful.

Allow me to explain when I create a piece, I have music playing in the background and allow the music to inspire the many colors and textures as well as shapes that I will use. As well as emotion and try to reflect this in my playing, it gives me a better understanding of a piece or composer as well as the emotions they are trying to emanate.

To combat nerves I do breathing exercises and meditations. This may seem odd but believe me it works if I meditate before a performance. I clear my head of all that stuff, and enter a place of peace and harmony.

I make it a point to go to concerts and study the violinists. Every technique is analyzed and then I replicate it when I go to practice

Well at conservatories they teach you ear training, theory, piano, harmony, history, etc. Some of these are more helpful than others depending on your field. I know that piano doesn't help me as a bassoonist but it sure does help me when I'm trying to arrange things for bassoon quartet.

Ear training doesn't help me calm my nerves while playing a concerto but it helps me diagnose what position I'm playing in a chord when I'm playing with the orchestra.

Theory doesn't necessarily help me with how to play my scales and all their modes but it might help me memorize a piece I have to perform if that structure makes sense to me and I make connections with the music and why it's written the way it is.

I also find that listening to other genres expands your musical range. Listening to jazz will open your eyes to really really cool harmonies, time signatures, orchestration, etc. Hip-hop will give you insight to different rhythms, grooves, vocal play, etc.

Also on a physical standpoint, EXERCISE, and maintenance of your body strength and flexibility is so important. As musicians we are ATHLETES. We have to maintain our bodies to be fit to play our instruments for as long as until we're even 80! There is a lot of stress that goes into body position, practice habits, muscle development, etc. So many musicians get tendonitis (I am not excluded from that either) and have complications so learning your body and how to keep it healthy is key.

Hope that helps, I could talk about this for days. Years.

I'm tending to view my playing to be a much more broad thing than just music. As self-important as it probably is, I want it to just be general art. To that end, I really want to immerse myself in all the differents things that artists all over the world put out there. Films, paintings, books, video games, clothing, I can be inspired by all of it.

Getting more to the "nuts and bolts", I absolutely find that more academic study of music (theory, history, etc.) totally enhances my playing. It just brings me out of the dark a little bit and makes me feel my place in time.

Swimming helps your lung capacity and breath control immensely. This is very helpful for the lovely horn note holds of 24+ beats.