Well, what's true, what isn't? I don't know, but according to Bustle. Season 2 won't just be about City of Ashes but will also introduce more of City of Glass. Like introducing the young werewolf Maia. That takes a liking on Simon.
According to Palameros we're going to see Will Herondale in the next season also. We're probably going to see Jace in a dark place for the first episodes of next season. They're going to bring the next level of Malec.
Jace (Dominic Sherwood) will be the lead in the second season. According to Ryan's Blog. It will be more about Jace than Clary. The site also says that the sister and brother story of Clary and Jace will end in the midseason of season 2.
Season 2 will be 20 episodes, like Pretty Little Liars, The Fosters, etc. Season 2 is expected to return September 18, 2016. While this can be fan fiction. Well all of this. Season 2B is expected to return in March, 2017.
According to Ryan's Blog Jamie Campbell Bower would be playing a part in the second season as a character that doesn't has a big part in the books or don't even exists. They would love to have him back for a season. After season 2 he'll probably be on a shows called Weaveworld. A young adult book turned into a show.
Clary, Simon and Izzy will have a big battle in the first season.
Again all of this could be fan fiction, nothing has been confirmed.