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: There has only been one research study looking at riboflavin alone. It reported that just over half of those who took 400 mg/day of riboflavin for 3 months experienced at least 50% reduction in migraine. Significant reductions in both migraine frequency and number of headache days were reported.
CoQ10: 300mg/day