Teeth whitening geel(its not that expensive and its very effective) or whitening strips which is a bit cheaper but still pretty effective unless you have very terrible teeth.Also floss and brush 2-3 after each meal,preferably use an electric toothbrush and purple/black toothpaste(they wont have a big effect but are better than normal toothbrushes and toothpastes).There are also other methods like coconut oil pulling but they haven’t worked for me but you could still try and see for yourself and its really good for killing bacteria so they dont make your teeth worse