Here are some ways to dissolve the mishris(sugar cubes) quickly-

1. By increasing temperature of the solvent(water), on heating the water, the water molecules gains energy(kinetic energy) hence moves faster and hence come is contact with the sugar pieces more often. thus more sugar pieces gets dissolved.

2. By stirring, the stirring procedure helps the water molecules to come in contact with the sugar pieces.

3. By increasing surface area of the Sugar pieces, further cutting the sugar pieces into smaller pieces increases the surface area of the pieces, for this reason the the sugar pieces gets maximum dissolving area and hence increase the rate of dissolving.