If you are confused, just do this:
Any downward motion in your melody must be made of either:
1:an indefinite amount of half-steps
2:whole-step followed by a major-third upward
3:a fourth followed by a whole step
Any upward motion in your melody must only be major thirds.
You can restart the lick from any interval that isn't any of the above after any cadence point, or after doing a downward "fourth followed by a whole step."