A general rule of thumb would be to position the bridge between the notches on each F-hole and then adjust towards/away from the fingerboard to suit your ear. That said, I’d recommend having your instrument set up by a luthier who works on a lot of fiddles/violins…they are worth the $, in my opionion. Best of luck!
Another way to check the position of the bridge is to measure the distance between the nut and the bridge (which is the vibrating length of the string), it should be around 328mm for a violin.
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