Brush twice a day with no exceptions. Easy routine: you go to use bathroom first thing in the morning - brush teeth and only turn leave bathroom. Same in the evening. If no time - get electric toothbrush. Better 30 seconds with electric toothbrush than not at all. Use whitening toothpaste.

Don’t use mouthwash. Many make teeth yellow. It actually hidden in small print on the bottle. Or look up which are ok.

I use SmileDirectClub Teeth Whitening Gel Kit with LED Light which I bought on Amazon. You use it twice daily for a week and then same every 6 months. One package lasts me for a year. That is about $50. It works.

For the other issues - you will need a dentist.