How does one know that Allah is pleased with him and that his prayer will be answered, and are there signs indicating that?

All praise is due to Allah, who has guided you to faith. Know that Allah has made His love and pleasure contingent upon the servant fulfilling certain qualities and deeds. You can refer to the mentioned fatwas (religious edicts) to learn more about the signs of Allah's love and the difference between His love and His gradually enticing (istidraj) with blessings. Delaying the answer to a supplication does not mean Allah is displeased. Allah answers supplications if their conditions are met and their impediments are removed, or He averts from the servant an equivalent amount of evil. For more on the etiquette of supplication, the conditions for its acceptance, and times of answer, you can consult the mentioned fatwas.