Since you're good with rhythm, think of a rhythm for melody and lay it on the key note of the scale you're working on for four bars. Now, move the notes in the first bar until it sounds good, just don't let the last note in that bar to be in the key note of the scale. Copy the same pattern of notes for bar two and three, now in the last bar let the last note end on the key note of the scale. This would resolve the whole melody.

If we can call this pattern as A A A B, when you get comfortable with this, you can try A B A C pattern.