Note: This is just for fun. I'm not doing this to attack any particular book or series. I just noticed a pattern and I thought it would be amusing to write a little bit about it.
How to Write Your Very Own Young Adult Paranormal Romance
Since most of your readers will be young women between the ages of 13 and 21, you'll want to have a protagonist in that age group. Make her about 18 or so; this way, the younger girls will have something to aspire to, and the older girls will have someone they can relate to. Your protagonist should either be a) beautiful, but unaware of her beauty; or b) beautiful and aware of it, but full of false modesty. In either case, your protagonist should have fairly low self-esteem. This will allow her to complain about her looks, inviting others to tell her how beautiful she really is. Your protagonist should be a normal human (as opposed to some sort of supernatural creature). If she is something other than human (or superhuman!), this must be withheld from the reader until the last couple of pages. Dropping hints is okay, but realize that your readers are probably going to figure it out long before you think they will. They're not stupid.
Now for the main character's love interest. He should be tall; this ensures that your protagonist will have to gaze up longingly into his eyes. He should have a good head of hair that can be described as "thick", "lustrous", or "flowing". These guys are never bald. Their eyes should have some noteworthy characteristic (and even if they're just plain ol' brown eyes, make sure you mention them as many times as possible). And in paranormal romance, this is the place for a supernatural creature. Whether you decide to make him a vampire, a werewolf, a shapeshifter, or an immortal, there are a few rules to keep in mind:
Paranormal creatures (especially hot, sexy ones) don't have bodily functions. They never go to the bathroom, even if they eat. Have you ever seen a werewolf have to excuse himself because his dinner of deer and/or wayward Boy Scout didn't agree with him? Of course not. This is because normal bodily functions are decidedly not sexy, so any mention of them should be avoided.
These guys always have a tragic past. Maybe they were beaten and abused as children. Maybe they lost the love of their life years (or decades... or centuries) earlier. Maybe they were turned into what they are against their will. In any case, they're now a wounded character. Milk this for all it's worth. Shows of sympathy from your protagonist (preferably involving gentle caresses where she brushes his flowing hair from his face) are a good way to do this. But remember... these guys don't want to talk about it. If you make them spill the beans too quickly, they might come across as... well, a little too girly for a leading man.
Don't worry about keeping to a particular set of creature traits, either. In today's fiction, you can get away with pretty much anything. Your vampire doesn't need to drink blood, sport fangs, and turn into a bat. One attribute is enough, and you can use the term "vampire" all you want. The same goes for werewolves, shapeshifters, immortals, fairies, selkies, mermaids, or any other paranormal creature. After all, you want to put your own spin on it, and you can't do that if you're hemmed in by conventions.
Whatever you do, don't come up with your own story! Stick with the tried-and-true. (There are no new ideas anyway, right?) The basic formula can be summed up in the following:
A hot new guy shows up at the local high school and seems to have eyes only for your protagonist. Your protagonist is both attracted and repelled by this mysterious teen hottie, who, of course, turns out to be some sort of supernatural creature. By the end of the story, they will be madly in love, and the girl will have been turned into one of her love interest's own kind.
The protagonist should vascillate between loving this paranormal cutie and wishing he would just go away. Don't forget, though: by the end of the book, she should have cycled back into loving him (if this hasn't happened, you need to add some more padding, some banal incident that will bring her back around).
Oh, and don't forget: all books in this genre must include a reference to Wuthering Heights. It's absolutely compulsory. The easiest way to do this (especially in young adult fiction) is to have the characters read the book in their high school English class. Then, let the dysfunctional relationship comparisons begin!
3. Writing Style
Write your book in the first person point of view (i.e., as if your main character is telling the story). You get bonus points if you write in the present tense. It just makes everything seem more immediate. With this point of view, the protagonist doesn't know any more than we do.
Make sure that your characters do strange things with their eyes. Have their eyes caress their lover's body, graze their surroundings, and bounce around the room. This adds an element of humour to the story, since such wording can be interpreted in a couple of ways. On a related note, break out your thesaurus when you're writing your speech attributions. Your characters should never "say" anything. They should murmur, whisper, screech, laugh, stammer, sigh, and shudder their words whenever possible. This helps give the reader an idea of how the character is feeling, and it cuts down on wordiness. Plus, it's fun for your reader to imagine what shuddered sentences actually sound like.
Finally, you'll want to create your own style and voice. An easy way to do this is to write incomplete sentences, repeatedly use that cool word you found in your dictionary and just had to incorporate, make up words, and use original punctuation. If you do these things, your readers will remember your book and your work will stand out.