The teeth are usually not yellow.
There is always some reason behind the yellow colour.
So without finding out the reason we cannot advice exact treatment plan for making or keeping your teeth clean or white.
But yes I will mention down few things for keeping your teeth white which is very general
1 brushing your teeth with a soft or ultrasoft toothbrush and using a toothpaste
2. Getting your teeth scaling don once or twice in a yr
3. Decreasing or being away form smoking and intake of soft drinks
4. If excessive yellow colour of teeth us there you can also go for teeth whitening.