Well, first of all, make sure you have a basic understanding of the Blue Exorcist universe. That way, you can better appreciate the fanfiction. Also, don't be afraid to explore different genres within the fanfiction world, like adventure or angst. And try to find fanfictions written by authors who seem to really know the characters well. You can often tell by how in - character the dialogue and actions are.
You can start from the chapter that follows the events of the anime's conclusion. Usually, it's a good idea to look for recommendations from fans or online manga forums for the exact starting point.
The character development is a great aspect to focus on. In fanfiction, authors often explore different sides of the characters that we might not see in the original work. For example, they might show a more vulnerable side of Rin Okumura.
Yes, the Blue Exorcist manga is over. It took readers on an exciting journey and concluded in a way that left a lasting impression. The final chapters brought closure to the characters and their adventures.