Stuff on voice leading and counterpoint would probably be what your looking for. There are specific books on melody, although they usually pertain to singing/vocal melody. Those are good too because an instrument is meant to simulate the human voice. Which is also why the best melodies are easily singable. Voice leading is where each note in a chord progresses to another melodically. Which if your looking for, how to write chord progression to melodies or vice versa, voice leading is how.

Melodies usually aren't complex, the complex part is the ornamentation.

Moving in steps is always good.
Sticking to skips in the tonic triad
Keep to chord tones on beats, except 2nd and 4th's which you shouldn't use too much.
Good melodies are easily singable, if you sing it and they're an odd interval. That's a very good indication you made a mistake.

Those produce good results.