.  Poke a small hole in your plastic  cup.  This needs to be big enough to stick your straw into.

Pour 1/2 part water and 1/2 soap into the bottom of your cup.  You don't need very much. In total, it will be about an inch.  Make sure your liquid is lower than your hole.

Stick your straw into your cup, tilt your straw so it is into the bubble liquid and BLOW!!