Alyssa You don't have to read any of Hocking's other books to read Frostfire! The Trylle trilogy (Switched, Torn, Ascend) is set in the same world as the Kanin Chronicles, but the Kanin Chronicles - Frostfire - features a different tribe of trolls (the Kanin), a different conflict, different (new) characters. There is some crossover, in terms of character cameos from the Trylle trilogy, but you do not need to read the trilogy at all to read Frostfire. You'll be fine! :)
Shilpa No you don't. I haven't read the prior series either and followed the story without any issues.
Kate If you haven't read the Trylle trilogy you can read Frostfire just fine, though if you plan on reading the Trylle trilogy at some point, Frostfire has a tiny spoiler about who the queen ends up marrying.
Sarah Lee You don't have to, there hasn't been anything yet that makes you go hmmm did I miss something however they are good books as well so if you feel you have the time start with them and work your way here. If you just randomly picked up this book and want to read it go for it!
Lori I felt like I was missing a lot of information having not read the other series in this universe.
Dani-Marie Watson It's true you don't have to read any other series... but the Trylle series (same basic world) is a really fantastic read, so if you like to read I'd recommend it anyways (even though you won't really need it to understand the new series).