Writing about animals in Middle Grade is easy*. Ten-year-olds dream about spending Saturday night with a new guinea pig or kitten. Young Adult main characters have busier lives, but that doesn't mean the family pet can't be very important. The family pet may be the only one at home whose opinion your main character still respects. Look for how dogs and cats are used in the novels you read. Here are some ideas:
1. Building sympathy for your main character. Is your MC the only one taking responsibility for Doggie or Kitty? Especially if there's tension at home, showing your MC is capable of great caring casts suspicion on the other members of the family.
2. Dogs as judge of character. Aren't dogs supposed to love good people and sniff out dangerous people? If that sounds too Disney cartoon for you, think of it in terms of a love triangle. If one of your love interests needs a leg up, the approval of the family dog is huge bonus points.
3. Indicating a big change. When a beloved family pet has to be given away because of the main character's changed circumstances, it's a sure sign that very bad things are about to happen.
4. Using the daily dog walk. Does it take your MC past an ex-boyfriend's house, a graveyard, a park where something awful happened? Or does someone else know her route too well?
5. Humor. I'm thinking of adding a ninja attack cat to my tween novel on its next revision. There's a lot of room for creativity here. For example, have your MC suck up to a smelly dog only to find out it isn't owned by her crush after all, but owned by ...
-- Kate, Miss Perfecting the Pages
* Well, not exactly easy. How about more obvious? Work with me here, people, I'm trying to make an analogy.