Everyone feels the jitters at some point in their career - some occasionally, some fight it every time they get on the stage. There are so many books written on the subject and many techniques available which can all be very helpful(Alexander Technique, Feldenkrais, Tai-Chi, Yoga etc).
Because of my interest in Psychology, I have read quite a lot on the subject and studied some of the techniques, but one simple thought is proving the most effective method for me at the moment which I will share in the hope that someone else might benefit from it.
When I am having a wobbly moment before a solo or before a delicate entry, I think to myself: I'm doing this because I love to play the oboe.
By reminding myself of this, I find that the fun and drive in my playing that has propelled me to where I am today in my career is what is actually the foundation of my authenticity, and helps to settle the insecure moments and to let go, thereby staying in the moment and serving the music without my ego spoiling the party. That's not to say that this will work for everyone, but for now it seems to work(most of the time) for me, so I thought I would share this thought. Give it a go - you've nothing to lose!