i know this has probably been said to you a million times but it is the truth...
practice recognising chords and their purpose. In basic terms, to differentiate between the tonic (the ending chord, closed sounded chord), the dominant (chord that pushes for the tonic), and the pre-dominant.
If that's all well and simple, I apologise because I don't know exactly how much trouble youre having.
Recognising and being able to identify actual chords eg I, IV, V, VI, ii etc, so that when you fill in the bass line, if you need to, you know what note it simply cannot be, considering you know what notes it SHOULD be.
If its general single line notes you have trouble with, try recognising the gaps by using familiar openings to songs you know well. For example, I always recognise the perfect 4th, simply cuz it's the beginning to "Amazing Grace", and now I don't need to cling onto that sort of support and recognise a perfect 4th straight away. You can try this with other pitches, including descending as well. With practice, you will recognise them well.
When in exam conditions, work out what is best for you after a few hearings. I think one of the hearings is without writing. Try to memorise the melody.
Some people find it easy when writing the answer to jott down the rhythm above the staves before tackling the pitch. This is a very good method, if you're capable of it. It ensures a decent amount of marks.
When in total doubt, try to go for the right contour and when it lands on the tonic note. It shows that even though you're not perfect, you have some good understanding of it.
Hope that helps.
