Finding the proper tire pressure for your bike can determine having a smooth and successful ride. It allows your bike to move as quickly as possible, and prevents those annoying flats.
Related: How to Fix a Flat Bike Tire
The best way to determine your proper tire pressure is to try out the manufacturer’s recommended pressure for the tire you own (it should be on a small label or molded into casing). The manufacturer's recommendation is usually in a suggested range. Ranges will end in psi which is the measurement of pounds per square inch. Narrow tires usually need more air pressure than wider ones which will entail a higher number psi. Also, body weight can determine a different pressure, a higher body weight will need a higher pressure. You should never go above or below the manufacturer's recommended range, but you can experiment within that range depending on body weight and comfort. Proper tire pressure will help absorb shocks and give you a more comfortable ride among bumps and rough terrain.
Some other factors to keep in mind are temperature, and weather. For wet, rainy days lowering your psi a bit can be helpful. Also, when the temperature drops it drops your tire pressure, and you should keep track, making sure you have the proper pressure before every ride.
Bicycle Sport Shop created this handy chart on their website that lists a basic pressure range dependent on rider weight and tire type. The road tire listing is for a basic 23c tire and the off-road is for a 2.0-inch width tire.