how to whiten my teeth?

Go to a dentist. really
all other home treatment will ruin your teeth

Use some White-out.

View attached image.

Dont try any aggresive stuff :L it can damage the protective layer... Just brush your teeth 2-3 times a day or go to the dentist

Just brush your teeth in the morning and after every meal (take your time) use a mouthwash+whitening toothpaste and also use mouthwash that has fluoride in it like 30mins after brushing, avoid foods and drinks that stain like coffee, spicy food, etc. :D

Visit the dentist regularly. Quit smoking if you do. Avoid dark drinks like cola and coffee etc as they stain your teeth (and if you can't resist, use a straw). Fruits like strawberry, apple and oranges have a whitening effect as well.

Brush teeth after meals... but not straight after them this might weaken their protective lamel just like using some agressive stuff (just less). Avoid baking soda, salt, hydrogen peroxide etc. This all will make your teeth change their color to grey in some time - and believe me it looks bad xD

If you wanna "do it yourself" method - use whitening toothpaste. They work, but they need weeks/months to make some changes (this takes so long that you might not even notice the change, unless you will compare photos before/after using it).

actully some people have yellowish teeth because of their genetics.you can't do anything about it
other then that brush your teeth 2-3 times a day

Drink milk everyday

just god damn clean them often, always clean before sleep, go once to dentist maybe for a special procedure, and then just dont drink coffee going to bed

Don't use your teeth, use a tube!

hydrofluoric acid! right down to the bone!

researchers are actually working on artificial enamel so i wonder how that will work out...

photoshop, you get excellent whitening without damage to the teeth.

i learned that if you floss everyday with dog hair your teeth will be as white as Obama

i have sensitive teeth, so i use a toothpaste called Sensodyne, and it's got all sorts of things to it. there's a complete care, repair one, normal whitening one, gentle whitening one, an extra whitening one, etc. just look it up on google images & you'll see all the options there are. or maybe the product website, idek, it's all up to you.

My friend swears by the otc one which costs like $35 to $40, US dollars, It comes in a square box, sorry I can't remember the name. I've used the ones from the discount stores, cost about $1.00 and they worked. Mine were bad from drinking a lot of black teas. It doesn't look like you are in the US, but there must be an equivalent at a local store.
and yeah stay away from soda. It's really bad, even diet is bad for your teeth. Studies say it can be as bad for your teeth as meth.
soda-mouth-can-look-a-lot-like-meth