Answer for colourwork:
I was having a look at Alice Starmore’s book “Charts for Colorwork Knitting” recently. It has charts relating to various colourwork traditions from around the world, but it also has a nice section on arranging motifs on a garment. (Most libraries should have the recent reissue, and, if not, you can usually request an interlibrary loan for a small fee to get it from another library network.)
If you are thinking of designing the motifs themselves, Knitsonik books have ideas on how to do this. (I haven’t looked at them in great detail but the ideas of using colours and themes from your environment seemed appealing in terms of sparking creativity.)
If you like the idea of unconventional, almost “punk” motifs, you could have a look at a movement called “hønsestrikk” from Norway.
Edited to add: Andrea Rangel and Tin Can Knits also have nice motifs and designs. Tin Can Knits have a couple of designs that are made for you to “colour in” yourself, with suggestions for motifs and colourways to get you started.