Avoid adding too much additional salt (in cooking and at the table), eat fresh food and avoid ready prepared meals which have too many additives. Trry not to have meals that have smoked meats (i.e. bacon), smoked fish or smoked cheese as these encourage fluid retention. Also wear comfortable clothes that are not too tight at this time of the month (elasticated waistbands and a supportive bra are ideal). If all else fails then see your GP about a mild diuretic but they are not the ideal answer.
Nurofen is usually good. If that doesn`t help then see your GP for a prescription for Mefenamic Acid (Ponstan).