Just watch your high-pop cities, and when they get to one food (with no available squares), survey the situation:
Can you improve food production?
If so, is it practical and desirable to do so?
If it isnt't, Can you stop woking one square now, to arrest population growth? This is an easier choice If there's a nearby city that can take the square.
For that matter, is another city holding a resource that will serve this city better? If you own the other city, weigh the benefits for each; if you don't...just park one of your units on that square
.
If none of the above applies, is it practical to send a food caravan?
I think that covers the options.