When do you put the verb in front of the noun in Spanish?

For example, in Spanish jokes I often hear something like this: Estan dos hombres en una casa. Normally, I'd put "estan" after "dos hombres" (Dos hombres estan en una casa.) Another example: Estaban en clases Jaime y sus amigos. Wouldn't you normally say: Jaime y sus amigos estaban en clases? How can you tell when to put the verb in front of the noun?