You'll need:

Use a basic heart cutter for the main cookie.

Use mini cutters like these and these for the varying shapes.

Plan ahead where you'd like to place the mini cookies on the main heart cookies.

Place a dab of glaze on the back of the mini cookies to "glue" them to the heart cookie.

Add dots, lines, dashes,swirls, flowers, heart, etc to your heart and mini cookies.

Use your imagination.

I had a lot of fun with this part. :)

Simply Valentine Cookies

Colored Dough & Simple Designs (Tutorial)

Rosebud Heart Cookies (Tutorial)  

Stacked Colored-Dough Hearts (Tutorial)

Decorated Stacked Colored-Dough Hearts (Tutorial)