Having a built-in light meter is the most convenient way to get proper exposure when using a film camera. Unfortunately, there are older cameras out there that don't come with one. My very first film camera (Leica M3) didn't have one, and yours might not have one as well. Today, I'm going to talk about three things that you can use to get good exposure without that light-meter built into your camera.
Light Meter App
The first thing I did when I got my Leica M3 was download a light meter app. I believe the specific on that I used was a called "Pocket Light Meter" for the iPhone. The way the light meter app works is it uses the light meter built into your phone and tells you what settings it is using. It lets you change different variables (aperture, shutter speed and ISO), so that you can tune it to the setting that you're using on your camera. You can then figure out what that last variable should be set at. I found that the meter readings that the light meter app gave me were pretty good, but I didn't like having to pull my iPhone app to take a shot.
Sunny 16 Rule
The second method I used is called the Sunny 16 Rule. This rule is based on the idea that during a sunny day, if you set your shutter speed to match your ISO (ISO 1000 = 1/1000 shutter speed), your aperture should be set at f/16 to get a good exposure. As the light drops, you drop your aperture 1 stop to compensate for it.
The Sunny 16 rule involves a lot of guestimating, but it is the method that I got along with the most when I was shooting with a meter-less camera.
Dedicated Light Meter
If you want to take it a step further, you can buy yourself a dedicated light meter. A dedicated light meter is crucial for getting your exposure bang on when doing serious work. With portraiture, for example, you'll be able to hold the light meter right in front of your models face to measure exactly how much light is hitting them.
Here are some of the more popular light meters that are still available new: