Bandcoach has mentioned some useful stuff, I agree to that. also:
Try not always to start on the chord's root note, starting on the 3rd note of a chords scale gives slightly fuller sound and a harmonic colour (depending if you're on minor or major), starting on the 5th gives you more tension due to frequency in tones.
Maybe use the so called "tensions", mostly the 9th, 11th and 13th tone of the chord scale you're on. But always check if the note you're using on downbeats (1 or 3 of a bar) are:
-either the 1st, 3rd, 5th or 7th (1st and 5th giving you less tension/tension without harmonic colour, 3rd and 7th giving you less/more tension with harmonic colour)
-or the 9th,11th,etc. if you're after clear harmonic tension in your melody, always doublecheck that the note you're using is not the b9 to your root note. Since tensions get a little complex, I'd suggest just use them when they sound right.
Another great arranging technique to blowing melodies: guide tone lines!! Most ppl don't even know what it is, but it's the connective tissue in melody and is used in every professional song.
The clue is, that over time youre melody develops in a special order. It can be very easy to create these lines, and it's yet so effective (on pop, rock, hiphop, jazz, orchestral, etc.). Simply explained: If you're having 3 notes that have an up movement (like arpeggio or chromatic or diatonic move) and that are spread over 3 bars, you can add a ton of other notes to your melody BUT these 3 Notes are either the highest or the lowest of this melodic motive and are the key notes of your melody (most likely placed on the downbeats.).
There can be just one guide tone line in the whole track or there is a guide tone line for every motive or even two, three, some just lasting a few bars, some last longer. There is no specific rule to these lines in melody that can be applyed to every genre (but in harmonic chords there is), but it's always good to use them.
Wow. Much text going on here. Try it out, may help you
(one very easy and hyper effective example: over the rainbow. Clear guide town moves, giving an upper and lower end of the melody.)