That is one of the things where Interval Theory can help.Composing using Interval theory is independent of Diatonic theory, but can enhance the diatonic system. With just one interval, like a 2 using complimentary interval. For example, a 2 in interval theory means 2 chromatic steps (a C to D). Something intervals do is their complimentary interval added will always equal the number 12. The complimentary is simply by taking the bottom note up an octave, and for a 2, the interval becomes a 10 (i.e., D to C which is 10 chromatic steps). So 2 + 10 = 12. That octave raised C note and the D below is still obviously the same notes as the 2, but the interval distance changed. Even though different, their sound will still compliment each other, but still have a quality that is different.
T.C. Jones, a Hollywood composer of many years, and composer Frank Hellinger started Music Interval Theory Academy (M.I.T.A.) teaching this method for comping up with ideas on the spot, along with many other methods using interval theory. With what they teach there truly is no way to ever have a problem with things like writer’s block.