#2- For girls- Find ways to encourage close in age shidduchim. Simply put that will give the individual a better chance of having someone to marry. Once againg I don’t know if this is a segula but it certainly helps the general klal as well as the individual.
for boys it is certainly a segula as chazal tell us helping someone in a situation that you yourself need help evokes siyata dishmaya in that same realm)