What is the best temperature to keep my thermostat at this winter?

i moved into an apartment this year with gas heat. this is the first time i've ever had to pay for heat. i was just curious as to the best temperature to keep it at or if i should only keep it on at night, or during the day or what? i've heard sooo many horror stories about gas bills being ridiculously expensive i want to try and cut down if i can. would a space heater while i'm home be a better option? i also have a dog and a cat and i dont want them to get too cold either. please help! its starting to get really chilly!