As an Asmodian the second instance you will be able to run is Fire Temple. In order to run Fire Temple you must first complete a quest called <Three Keys> to get attuned. You can see my guide on Attunement to the Fire Temple here.
When you get Attuned to the Fire Temple be sure to grab the quest from the Shugo outside before entering. He can be found just south of the entrance of Fire Temple. The quests he will give you are "[Group] Kalgolem Crystals" and "[Group] All Nyerk and No Play". However only the Kalgolem quest is for Fire Temple.
There is also a quest that comes from Bulagan. It is called "[Group] An Ancient Weapon]". It requires you to loot an Ancient Treasure Box in Fire Temple for an Ancient Weapon. Once you have these quests head north to the Fire Temple itself.
Silver Blade Rotan
The Silver Blade Rotan wonders around the instance. You can't miss him though he is a very unique looking mob and pats nearby the second boss. As with the other two bosses in this instance Silver Blade Rotan is a very simple tank and spank fight. He drops a ring with some Magic Boost and HP on it.
Tough Sipus is a rare spawn in Fire Temple. He is can be found right around the corner from the last boss. Tough Sipus is a very basic tank and spank. He is most commonly referred to as the "Shield" boss since he drops a decent shield. Tough Sipus will come with 1 add that you should CC or kill first.
Kromede the Corrupt
Kromede the Corrupt is the boss of Fire Temple. She is a pretty simplistic tank and spank boss. The only unique thing that she does that you need to watch out for is her AoE abilities. When she starts casting all melee except for the tank needs to get away from her. Or they will be blasted with an AoE that hurts. The AoE will also but a DoT on anyone hit by it which can be dispelled or cured.
NOTE: There are other bosses in Fire Temple however these 3 are you average run. I will cover the rest of the bosses when I can actually get a group to fully run it.