To combat this I sometimes find an image, or clip of film which embodies the vibe of the piece, and I use it as an anchor to make sure I don't drift lazily to my default position. Something you can look back at and check you are still aiming in the same direction.
I think that book by David Byrne solidified my ideas on combatting this problem.
http://www.mcsweeneys.net/articles/a-mc ... usic-worksChapter One
CREATION IN REVERSE
I had an extremely slow-dawning insight about creation. That insight is that context largely determines what is written, painted, sculpted, sung, or performed. That doesn’t sound like much of an insight, but it’s actually backward from conventional wisdom, which maintains that creation emerges out of some interior emotion, from an upwelling of passion or feeling, and that the creative urge will brook no accommodation, that it simply must find an outlet to be heard, read, or seen.