don't copy tomic's serve. it's not even wta level.
if roanic's style doesn't suit you copy sampras, roddick, federer and such players, or someone who has similar height as you and is a good server. there are so many good options to choose from.
Disclaimer: I'm NOT a coach...
Real tennis: https://www.youtube.com/watch?v=yDqnkLJ9BtM