Ideally, you want your cities tiles to be as productive as possible, because the more population a city has, ultimately the better. BUT... if you have a high growth city, you will need to control its pop growth somewhat or you will begin to run into the problem of unhappiness/unhealthiness. I had a city in my last game tucked in between two rivers and all tiles were flood plains(wheat on one) except for two plains tiles and 2 hills (gold on one of them). quickly grew out of hand to the point where i did two things: used the city governor buttons to emphasize production(effectively moving citizens to mine the hills and workshops) and stop growth( which put several pop into citizen specialists) as more health and happiness resources became available, I was able to slowly let go of the growth stop and let her build up. End game, that city out produced all my other cities(including capital) in research by alot!
Don't be afraid to use specialists, their bonuses will begin to add up significantly.