Most importantly, try to have the marriage when the moon is in a nakshatra that is dhruva. They are the three Uttara, and Rohinī.
If possible, on top of that, when the moon is at least half full. Ashthami (half full) is ideal. Waxing is better than waning, but avoid the 11th phase (ekadaśī). Waning is OK if it is asthami or prior.
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