VIOLINIST HERE!!
hmm, i think that, true you must have great foundation with your technique, but you must be expressive, i remember observing the girl i accompanied for her violin piece last year for her HSC, she stood like a block of wood, with good intonation and technique, but it was much too boring (she played a tango), body language and the emphasis of your knowledge of the piece is important!
When trying to communicate the music through body language, dont move too much or awkward, try to do it in an expressive way...maybe get your teacher to teach you that if possible, and nice bow gestures when starting and finishing the piece will make the performance look that much more better.
Know your music! for instance, dont crescendo and decrescendo randomly in a baroque piece as they tend to have a unity of mood/rhythm/dynamics, though if the dynamics were to change, its usually sudden (terraced dynamics = soft (p) to loud (f))
so know what you play, research the piece and its composer, see if there's a story behind it and try to express it how the composer wanted it to be expressed.
and good intonation always helps :>