The making of Post it, step by step...

Fisrt, the background.
A wood texture for the desk.

Cut the hand with the card

add some light on both background and hand

Considerating the light comes from above, Correct the shadow from the hand and, incline it, colorize the paper in yellow (after giving it a little curb) And then add some thickness under the paper to give the impression it's a block of POST IT

Why not addding a pen (and give it the right light and shadow effect)

Now write whatever you want on the paper ;-)
Create also some shadow under the hand.
And here's the final result. Hope you like it !