Most people will not notice that their teeth are becoming discolored. It happens so gradually that it is unnoticed day to day. When a person does finally notice or gets told about their stained teeth they then go to the dentist to have them bleached. Bleaching is a harmless treatment in which hydrogen peroxide jelly is used to remove the stain that collects over the years. It cleans deep into the tooth . It does not damage the teeth and can be done in the office (in about an hour) or at home. Then the process happens all over again. There are ways to get off this merry-go-round. One way is to bleach at home. I would recommend a dentist made tray and a person wears it for a couple of hours every four to six months. The upside is the teeth stay white. The downsides teeth can become sensitive. Another issue is you have to keep buying more gel.
If a person doesn't want to do this can brush their teeth with baking soda. This will remove the stain sitting on the tooth. Salt works , but, if you have high blood pressure then this is not for you.Diatomaceous Earth powder is good stuff too. All of these things will gently scrub your teeth without being too abrasive
Don't under any circumstances use lemon juice or any other acid. It doesn't matter if it is natural or not. These caustic liquids make your teeth whiter but do it by removing the calcium. So whiter yes but also softer.
Whitening toothpaste and rinses are a waste of time and money? They don't work. If you are bleaching the teeth get gel from a reputable source. I have heard charcoal works but I think it does because of it's slight abrasiveness. I don't believe it works because of any intrinsic properties.
If you have an occasion to attend, I have had patients who had job interviews come in for a scrubbing. They didn't want to bleach but wanted clean teeth.