If you’re shooting film and don’t have a light meter – use the Sunny 16 rule

This works for digital cameras too of course, but I’m not sure I’ve ever seen a digital camera with no meter.

Anyway assuming its “sunny” outside, set your aperture to f16. Then match your shutter speed as close to the films ISO as possible. For example if you’re shooting Fuji Velvia 50 (ISO 50) set your f stop to 16 and your shutter speed to 1/60 of a second (close to 50 as we can). You should have a good exposure. If its a little cloudy open up to f11 and if it’s overcast open to f8.

For Kodak tri-x (ISO 400) set your shutter speed to 1/500. Adjust for different film speeds in this keeping.

Always bracket important shots, but you’ll start to learn to see light value and expose without a meter.