The game's title includes an allusion to a conspiracy, the Masquerade. Secrets are an integral part of the genre. So City Secrets isn't all a Storyteller should consider. Kindred seem more real to me if they have secrets of their own to hide.

For every Storyteller character I write up one or more Personal Secrets. Merits & Flaws are a good place to look to start inventing new Personal Secrets. This must be something the character doesn't want anyone else to know about.

Personal Secrets are a great tool to represent the paranoia and horror of the game. Some are mundane, some supernatural. They can be political, social or physical. Here is a list of some Personal Secrets I came up with.

The character...

• has powers outside her clan.
• poses as a lower-generation than she really is.
• acts like a different clan than she really is.
• was Embraced by an opposing sect.
• deals with an opposing sect or enemy group (like Lupines).
• studies an opposing sect or enemy group.
• is Blood Bound.
• has broken a Blood Bond.
• actively conspires against a major character or an entire clan.
• idolizes another Kindred.
• wishes to sire progeny, or already has against the Prince's will.
• plots to become Prince.
• is hunted by someone powerful.
• accidentally learned another character's personal secret.
• knows about sect secrets she shouldn't.
• runs a blood cult.
• hates members of the opposite sex.
• is in love with a mortal or another Kindred.
• still tries to have sex, eat food or maintain a mortal existence.
• feeds on other Kindred's retainers.
• steals from other Kindred.
• is a carrier of a disease.
• has a derangement.
• has committed Diablerie or wishes to try it.
• has destroyed an elder.
• is an infernalist.
• voluntarily Frenzies whenever she can.
• is losing control (Humanity is falling).
• is becoming soft (Humanity is rising).
• is contemplating suicide.
• hates being undead or a vampire.
• feels out of touch with the modern age.
• is very unlucky.
• is a failure, or thinks she is.
• is terrified of her own Sire.

Personal Secrets are simple until you start using them and designing them to fit your characters. Don't just pick one from the list; invent one for each character.
Here's an example:

I had an angst-ridden Gangrel named Franco running with the more macho Gangrel in the city. Definitely a follower, I needed something secret to flesh him out. I decided the character hunts in wolf form, and wolves don't wound - they kill. So when Franco switches to wolf form, he hunts down prey, kills it, and drinks its blood. Occasionally that prey is a human and he feels guilty over it, but rationalizes it as his other side doing it, sort of like a split personality.