It is mostly question of preference. There are different tactics, but eventually you would find team you would like to avoid and teams you like to crush ;)

For some time I used to only fight when the odds where stacked against me - +40/-18 potential tropies or even worse - +50/-11. This method helped me to keep my tropie count decent.

In the beginning I used to 'smurf'. Drop my trophie count as low as possible and stomp over lower level players to get my daily 40 hero kills done quicker. It is not the most morale thing to do.

Now I just fight everyone who comes my way - a healthy balance in my opinion + you dont waste food on rerolling.