The honest answer, as both a parent of a girl with autism and an experienced teacher, is I never quite found the answer.
The strategies are space (tiny room?), bullying policy (are the senior leaders playing their bit as well?), talking (all your time there's 29 others?).
I have had some success with:
-visual sign, e.g. Ruler with a red side. Child holds it up as soon as someone is mean, you very quickly deal with the issue. Holding the ruler up gets a reaction.
-very very strict no touching policy for the ASD child also, that leads to instant time out. Shouting etc or other things slide, but this is the no no. It does work in time (controversial I bet). ANY touch=time out the room instantly to cool off, other explosive reactions are deal with calmly.
-talking to child with ASD about THEIR non-neogiables/ triggers, what are the persistant things done each time that always tip them over the edge. Apply the same zero tolerance to other pupils for this, e.g. even a whispered 'who do you fancy' to the child=immeadiate internal exclusion. Display these if you have too in words or pictures, let child with ASD reference/ point at them. Allow around 3 for clarity, you'll find many actualy have a few senstivities that are constantly picked on (eg fancying boys/ gait) and can ignore other things/ ask for help calmly.
-would headphones during independent work be possible? Ear buds and stick to non-popular music makes less fuss for others I've found, eg classical and nothing catchy to sing to if others want to hear.
-fiddle box? Box of bits, or pencil case
-is there a buddy child they enjoy sitting near? Would they actually like their own space?
-whatever you do, I've found visuals excellent to catch the eye of the child. Such as signed class rules/ individual pupil agreements/ a visual sign they can use to get attention
lastly, go and haunt the SENCO without shame...