Rhythm of Secondary Melodic Lines
When trying to find a secondary melodic line to a main melodic line (e.g. you have your main melody in the strings but want an independent horn line as well to support it) try shaping that secondary melody in a way that it moves on different rhythmic moments than your main melody. For instance let’s say your main melody moves mainly in the rhythm quarter-quarter-half note, you wouldn’t want your secondary line to move close to that rhythm as well (as it will also make it trickier to distinguish the melodic movement). In this case, it might be a good idea to have your secondary line move rhythmically during count three and four (where your main melody sits on a half note). It might also be a good idea to have your secondary melody tie notes over bar lines to counteract the downbeat-heavy main melodic idea and help working against the statics of the main rhythm.