I`ve been playing viola for almost 4 years, but I never learned to do a proper vibrato. Since I`m going to be playing a solo at a concert pretty soon, I was wondering if anyone could give me some helpful tips? Thanks

There are different ways to do vibrato but most people just pick it up naturally...just work on it.
I personally use my wrist.I started on my 4th year too. I`m now on my 7th year but for violin and it`s probably it`s best right now. It can take some people awhile to learn but we all have different durations. goodluck

What I`m having trouble with is: how do you vibrate your wrist without moving the whole viola? That`s really annoying! I have the motion down but I can`t seem to keep the viola still!

when you do vibrato, your hand should hang loosely on the neck of the viola. There should be like a little window made by your thumb and pointer finger under the neck. Start out with slow excercises, like playing eight notes by vibrato( slow vibrato) then vibrate a little faster (sixteenth notes). And once you accomplish that, you can proceed to 32nd notes. You should use a metronome.