I’d definitely tell my kids to stand up for themselves. Bullies pick on people they see as weak. So my goal would be to make sure my child is the least weakest kid in school.
I’d teach my child to verbally fight back with insults if they were insulted but never escalate to physical unless the bully escalated it.
If it ever gets physical, use everything you have to fight back. Eventually, the bully would see it as too much trouble to release whatever insecurity they have into my child and give up.