The max pressure is embossed on the tire's sidewall. I always pump up my tires to the max pressure. This reduces rolling resistance and also gives you the maximum protection against pinch flats. Some people back off the max pressure a bit. Try a few rides at the max before you do this. Then, back off 5 psi at a time. Don't back off more than about 10 - 15 % of the max pressure.
Check your tire pressures often. Pressures can drop 10 psi or more overnight. Personally, I check tire pressures before every ride. With a floor pump, it just takes seconds.
HTH