How can one determine their destiny, whether it is to Paradise or to Hell? And is there a specific prayer or method, like Salatul-Istikhara, to communicate with Allah to calm obsessive thoughts?

The destiny of a servant, whether to Paradise or Hell, rests solely with Allah. The believer must live between hope and fear, striving in obedience and shunning disobedience. Whenever they find themselves successful in acts of obedience, they should rejoice in goodness, and if they find the opposite, they should hasten to repent. The way to strengthen one's connection with Allah is to strive in worship, by performing the obligatory duties and then the supererogatory acts. Among the greatest acts of worship is prayer, for it is a connection between the servant and their Lord. By the measure of this connection, the doors of goodness are opened and the causes of evil are severed, and success and goodness overflow upon the servant.