What comes next?

Whenever I'm writing something and I do a PAC (perfect authentic Cadence) (( V7 - I with leading tone in soprano)) I always have trouble finding what comes next. it's such a ultimate sound. what I want to know is what, "Y'all" do to maybe add on to the piece after a cadence. Something like a key change or a new phase or what ever. and if it's a key change i'm curious to hear what common modulations are. As in a tonal shift ( and by what scale degree) or a common tone or pivot.

Thanks! 

In classic harmony, the perfect cadence is usually reserved for the end of sections and the end of the whole piece.

Between phrases or periods, semicadences are preferred.

Modulation can be done suddenly, or you can write a transition to reach the new tonality softer.

When these key changes occur, it is frequent to modulate "further" for a short phrase and back to the definitive key. For instance, if you are in C major and the next part modulates to the dominant G major, it can be done this way:   C major (key) -  D major (dominant of G, and an additional accidental) - G major.