"Once you face the lion, it will turn into a kitten"
To start off with, play through your piece once, identify scary (lion) parts, and highlight them in a “non-threatening” way. I usually draw red hearts around them :) Once you have highlighted the sections, it’s time to turn the lion into a kitten- in other words- make it less scary. Below, I have listed a few strategies; I recommend you trying one per day:

The Lazy Lion:

Play in slow motion and breathe through the melody as you play. This will relax your body and help you prepare every movement carefully.

Lion with a Party Hat

Perform a section in different styles (classical, romantic, jazz, fiddle, etc.). Be silly! Overdo it! Laughter will relax your body. Focusing on style rather than technique will take your mind off of technical challenges. 

Dancing with the Lion

Sing through difficult sections while dancing, walking, or shaking out your hands or legs. Singing will not only help you get familiar with pitch, bow speed, rhythm, or phrasing,  but will also get you used to breathing through the entire section. If you move continuously while singing the melody, physical release will automatically be triggered once you actually play it. Side note: if a section is too difficult to sing, listen to it while moving around in the room.

Roaring Back

Make a difficult section scarier by either transposing the melody (playing in a higher position), speeding up the bowing, or adding physical movement (like walking around the room)- play the section twice and then return to playing it the way it’s written.

Lion in a Pink Tutu

Turn a scary section into a “second movement.” Convince yourself and your audience that what you are playing is part of a slow, romantic section. Vibrate every note, play musically and lyrically.

Making the Lion Disappear

If you can't see the lion, it's not actually there, right? This also works with difficult sections. If you can't hear yourself play, you are less likely to tense up or worry about playing out of tune. Play air violin for a change! Listen to a recording while "playing along" just above the string. If the tempo of the recording is too fast, slow it down with this program: http://onlinetonegenerator.com/time-stretcher.html