personally for proving questions especially trigo, i reckon u memorise all of the formulas, esp double angle and half angle.
also, for other types of proving qn like prove d = 1/2 in an a.p, u can always go back to your basics, which is U1 + d = U2.
but, i would say that as long as u practice a lot of questions u should be able to recognise how to prove the questions
