If we can't do this then auto focus can help. Also, you can use a measuring tape to find the distance from the subject to the film plane of the camera and manually set focus. Some older cameras such as the Nikon F3 or FM2 provide a thru the lens metering system that tells you when the exposure is too short, too long, or just right. Of course the metering systems of cameras despite marked recent improvements can still be fooled. There are several reasons for this.
Prints are second generation images.
You lose resolution when you go from the negatives to the prints. Also the photo finishing places that handle prints will try to guess what you intended when they make the prints. Images you deliberately made dark will be lightened. Images you made light may be darkened. If the lab thinks the colors are wrong they will attempt to fix them.