What are invocations? In a real sense these are requests which come from the bottom of our hearts to Allah Almighty. Allah is always ready and happy to receive prayers from anyone at any time.
If you're facing any difficulties or trouble you should immediately turn to Allah for help. The best invocations are those narrated by the Prophet (S). If you don't speak Arabic, you can pray in your mother tongue.
When we pray we should feel assured that Allah will accept our requests. We should do so with complete sincerity and devotion.
Prayers can be made at any time, but there is a greater possibility our prayers will be accepted if we do so at specific times...
Taken from the Publisher's note.
