I am facing a lot of problem in proving trigonometric results (advanced ones). There are a lot of formulas (compound angle related ones, transformation of sum into product ones and vice versa, multiple angle and sub-multiple angle ones). I am unable to figure out how to proceed forward in proving results and what formula to apply. I got 0 out of 20 in my exam on trigonometry. I would be very grateful if someone could provide some suggestions (which are helpful and applicable in almost all situations) on how to decide what formula to apply and how to proceed in general. I am sorry if my question appears to be too broad. I have not asked about any specific problem because that would be of little help to me in other problems.