Find the vendor list and research the sellers before you go, as expo managers don't vet vendors to ensure they have good reputations.
Bring a friend who can stop you from impulse buying.
Go with an idea of what you want and how much you are willing to spend.
Do not ask to hold an animal unless you fully intend to buy it.
Don't touch or lean on the tables, this is a good way to transfer mites.
Bring cash.