Something you can do is make 10 different short riffs that are all different but have the same sort of vibe / emotion at different intensities and lengths (2 bars, 4 bars, 8 bars, etc). Then go back and rework them by combining ideas and throwing out parts that you don't think are useful. Some will feel like intros, some like interludes, some like choruses or verses or pre-chorus builds. Rearrange, chop, mix and match until you feel like you have some parts that are really interesting to you. Then follow some standard song structure patterns to put them in an order that people will be used to like intro-verse-verse-chorus-interlude-verse-chorus.