to clarify what it meant where i rambled on about the treatment of "melody", if it's not a straight scale (which you can spell without a gap, which if made up of less than seven tones is omitted where necessary) you just have to spell it in a way that outlines the shape of the ornament. bb because the step movement of a trill on a should reflect on the notation. same goes for any other melodic effect. auxiliary tones are like trills, passing tones have been mentioned by every other follow up post, appoggiatura should be approached by leap and resolved by step, etc. etc. to make things easier, the new tone shouldn't be on the same line or space unless it's an anticipation, suspension, retardation or pedal if not playing the role of harmonic alteration (chord quality for example, in c major to minor, e to eb instead of d#) and things like that. as for chromatic lines it'd help to spell them in a way that the chromatic tones fill up as passing tones between the notes of the scale which have been fixed in place by the "no gap rule". try to allow two unique pitches on the same line/space on a chromatic scale (c# d d# e as opposed to db d d# e). hope you'll find this helpful enough.