You can't... at least science has never found proof that it's possible. It's fiction.
Sorry to break this to you, but vampires are not real, and there is no ritual to become one.
Dakota: No one knows how he became a Vampire
no one must know anything
No, you do not. You can only become a vampire by being bitten by one, either contracting Porphyric Haemophilia from vampire enemies, or by allowing Vicente Valtieri to turn you into one.
One Vampire can bit you
no one must know
the only way is to have one human and one vampire parent.
Well, one of your parents has to be a vampire, one a human, so when your born your human-vampire hybrid.
You become a vampire if you get bitten by another vampire
You can become a vampire if you meet one and become friends until it bites you, but to fly like a bat you click a spot (as a vampire) and choose 'fly here'
You cannot make a spell or potion to make yourself vampire - you can only become a vampire by being bitten by one.
They must get bitten by a vampire. Some say a spiritual ritual will make some one a vampire.