Try them for 3 months. If they are not of benefit then they are not for you. Keeping a headache diary may help figure this out.
The following information was taken from the Nationalmigrainecentre.org:
Magnesium: Magnesium Citrate 600mg per day. Different forms of magnesium accomplish different things.
Riboflavin: Vitamin B2 400 mg/day for three months supplementation has been shown to reduce days, duration, frequency, and pain score of migraine attacks.
CoQ10: 300mg/day