One thing I like doing is having a plot matrix, marked up with involvements, and whether the inclusion is active or passive.

For smaller games, try drawing this as a wheel, and using different colours for each type of plot and relationship. You're looking for overall balance, not for each colour - for instance, some players might not be given (eg) romance, to better match casting.

I also have a bit of a hobby-horse about writing GM-view plot summaries.